Part of the problem with drawing conclusions about 'Oumuamua is that it's the first interstellar object we've detected in our solar system. Because of that, we don't really know if 'Oumuamua is a regular kind of interstellar object or a strange one. Presumably in the near future we'll be detecting more interstellar objects. If a lot of them look like 'Oumuamua, we can probably assume this type of object forms naturally. On the other hand, if we don't see any more that act like 'Oumuamua, then maybe it's worth looking at more unlikely possibilities (like it being an alien solar sail).