I mean, it's conceivable that there could be some unknown thing that curves space in oddly specific ways that look just like matter, and also kind of moves in b

I mean, it's conceivable that there could be some unknown thing that curves space in oddly specific ways that look just like matter, and also kind of moves in bulk like matter, but that would be drastically crazier than even dark matter is, so no one should expect it to be more likely.