Because the phrases he wrote on the bullets are linked to groyper shitposting/slang. If you read this, you are gay LMAO is also not something a left wing person would typically say, but more than that it makes anyone making serious arguments about the shitposts look pretty foolish. This was not someone who was making serious political proclamations, thats pretty obvious.  You are right that just because he was raised in a conservative household doesnt mean he was necessarily conservative himself, however it does make it statistically much more likely. I think we are dealing with a person who as terminally online and radicalized by online spaces like 4chan and possibly Nick Fuentes groyper culture.