If it truly was for political reasons,
1.you'd have to have a clear message for why you committed the crime. that's the point of domestic terrorism, to send a message, to bring attention to your political goal. maybe we have to wait to see if some manifesto comes up or more information comes out for why he did it.
killing random civilians for leftism just doesn't make any sense to begin with. for example the el paso shooter specifically went to el paso to target hispanics because he believed hispanics where replacing white people. there is no clear reason why someone looking to promote leftist ideology would target random civilians in some random neighborhood, unless it was of course to send a message about his ideology, which we yet to see.
He killed his sister. that alone makes it seem unlikely it was purely for political reasons.
apparently made a hit list in highschool: and was suspended for it: https://time.com/5643875/ohio-shooter-connor-betts-hit-list-rape-list/
I think it was for some sort of revenge. Shot up a specific neighborhood wich includes his sister. Had previously made a hit list and got suspended for it.