There's definitely not enough evidence to say Oumuamua is an artifact of an alien civilization. But there isn't enough evidence to say it isn't either. Moreover, as far as I know, there is enough evidence to be pretty sure every other significant celestial body is not an alien artifact. So it's higher on the scale than anything else.
The argument I've heard is that it is a disabled alien probe. This makes sense given that any device sent into space will probably last much longer as space junk than as a working device. So, the density of alien space junk would be higher than the density working artifact. Thus, if this thing were to turn out to be disabled alien probe, it would be more or less what you'd expect to see occasionally if alien civilizations of our level existed in some moderate density (note, most of "Fermi Hypothesis" possibility arguments involves hypothetical higher levels of civilization, which seems to me a rather thin argument).
The argument I've heard is that it is a disabled alien probe. This makes sense given that any device sent into space will probably last much longer as space junk than as a working device. So, the density of alien space junk would be higher than the density working artifact. Thus, if this thing were to turn out to be disabled alien probe, it would be more or less what you'd expect to see occasionally if alien civilizations of our level existed in some moderate density (note, most of "Fermi Hypothesis" possibility arguments involves hypothetical higher levels of civilization, which seems to me a rather thin argument).