Thanks for the link. Always good to hear the other side, especially after listening to the Lex interview a while back. Here's the summary:
Loeb's argument for Ouamuamua being aliens rests on 6 observed anomalies. All but 1 or 2 have pretty reasonable rebuttals.
[1]: Anomaly: There are too few interstellar asteroids to expect something like this, so it must have been aimed at us. The brand new telescope that discovered this was designed to look for interstellar rocks like this, but the fact that it discovered one so quickly is absurdly lucky.
Rebuttal: Most models for interstellar rocks could be wrong. There are some models for interstellar rock ejection however that would put this observation right in the zone of reasonable probability.
[2]: Anomaly: Ouamuamua is flying in a vector called the Local Standard of Rest (LSR) -- it's not "flying" through space, but rather looks like a stationary beacon or 'buoy' (aliens speculation: comms or navigation station). The LSR is basically average orbit around the galactic core -- all local stars are bouncing in all directions, but if you zoom out, on average, everyone's orbiting the galactic core. This average is the LSR, and it's weird that Ouamuamua is right in the LSR range.
Rebuttal: LSR is exactly what you would expect for an interstellar asteroid. Interstellar asteroids are formed early in solar system development, when gas clouds are still condensing into stars and planets. Those gas clouds are traveling around the galaxy in the LSR range, so anything ejected during that time should be in the LSR range.
[3]: Anomaly: Ouamuamua had an unusual orbit and flew close to Earth, so it must have been aimed at us.
Rebuttal: Observational bias. Had it not passed so close to us, we wouldn't have seen it. Given that within only a few weeks it all but disappeared from detection capabilities while still well within the solar system, it could be there's lots of other objects like this currently in the solar system that we just haven't detected yet.
[4]: Anomaly: Ouamuamua is too reflective to be a comet or asteroid.
Rebuttal: Straight up disagreement. Other scientists to point to comets and asteroids that could have that level of reflectivity.
The last two arguments are the interesting ones where the rebuttals are a bit weak.
[5]: Anomaly: Shape is too strange to be natural, but could be a thin solar sail, tumbling perhaps due to being derelict. It was too small to resolve with any telescopes, but by curve-fitting brightness shifts, models suggest it's either cigar-shaped (popular depiction) or pancake-shaped (the solar sail hypothesis).
Rebuttal: It does have an anomalous 6:1 brightness shift every 8 hours, but a tumbling solar sail should have an even higher contrast ratio. If it was a solar sail, it would have to be gently wobbling, not completely tumbling. This is actually what we'd expect from a solar sail (keep it more or less pointed at the sun), but if that was true, we would have expected the brightness fluctuations to even out as it got further from the sun (angles and geometry). This was not observed, so it probably kept tumbling, therefore not solar sail.
[6]: Anomaly: It exhibited acceleration that couldn't be explained by gravitational forces. Comets have this acceleration because a comet's tail is outgassing of the ices that make up the comet, acting as a rudimentary thruster. But Ouamuamua didn't have any observed tail, therefore, solar sail.
Rebuttal: Basically some kind of new comet chemistry that would have prevented us from observing the comet tail. Some gasses would have been hard to observe, or the outgassing was lagged so it started after we would have been able to observe it. Basically, "we haven't seen this before, but there are hypothetical ways to explain this." Science, and astronomy specifically, is filled with those kinds of "we haven't seen this before" discoveries.
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This is my summary of the youtube video, which is a summary of a few papers... to go deeper, should probably read the primary sources. I'm also just a youtube watcher, not an astronomer.
In the Lex podcast, Loeb kept quoting Sherlock Homes: "If you exclude all other possibilities, whatever remains, however improbable, must be the truth." My take is all of these rebuttals do seem to include other more prosaic possibilities, so Loeb hasn't really excluded all the other possibilities that warrant the jump to the improbable.