I think that by "can guess fake words" in the title OP means that the tool can come up with a plausible guess for the etymology, even for fake words. Unfortunately, the more common reading of that phrase is that it can tell fake words from real ones
Agree. It does a good job at coming up with a plausible meaning of novel words like "multiarborality" → "the state of relating to many trees" but it doesn't indicate that this is a "fake" word even though I just made it up.
I don't even know what a fake word is.
https://deconstructor.ayush.digital/w/flonkers
"Flonkers: A made-up word, likely humorous". Aren't all words made up? Edit: This one, unlike my previous example, is actually in use - flonkers: an animal that looks fat but is actually just fluffy.