Comment by ceejayoz

> We'd assume they're mostly like our comets due to the Copernican principle.

We're still figuring out what our comets are like, let alone unusual ones spending a few million years in interstellar space. New types of comets(ish) bodies discovered in the 2000s:

https://en.wikipedia.org/wiki/Active_asteroid

https://en.wikipedia.org/wiki/Manx_comet

We've spotted ~5k out of an estimated trillion. Each one we've sent a probe to has brought surprises. The Oort cloud remains theoretical at this time, and the first Kuiper belt object other than Pluto/Charon was found in 1992. It would be deeply silly to think we know everything about our local comets, let alone unusual ones from elsewhere.