He's numerically sound (astrophysics is
a lot of math) but stretching things on alien interpretations.
His wikipedia page captures both facets:
Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University. He had been the longest serving chair of Harvard's Department of Astronomy (2011–2020), founding director of Harvard's Black Hole Initiative (since 2016) and director of the Institute for Theory and Computation (since 2007) within the Harvard-Smithsonian Center for Astrophysics.
Loeb is a fellow of the American Academy of Arts and Sciences, the American Physical Society, and the International Academy of Astronautics. In July 2018, he was appointed as chair of the Board on Physics and Astronomy (BPA) of the National Academies,
and:
In June 2023, Loeb announced the project had found interstellar material on the ocean floor..
These claims were criticized by other scientists as hasty, sensational, and part of a pattern of improper behavior.
Peter Brown, a meteor physicist at the University of Western Ontario, argued the material can be explained as non-interstellar, [...] Brown further said he was disturbed by Loeb's lack of engagement with relevant experts.
Astrophysicist Steve Desch, at Arizona State University, commented "[his claims are] polluting good science—conflating the good science we do with this ridiculous sensationalism and sucking all the oxygen out of the room", and said several of his colleagues are consequently refusing to engage with Loeb in the peer review process.
As noted elsewhere about a competant brain surgeon believing pyramids to be hollow, it's entirely possible to reason well about physical forces and black holes and to also be utterly incorrect about material science of metallurgy.
quotes from: https://en.wikipedia.org/wiki/Avi_Loeb