I think this is looking for something to nitpick about. Of course he has an arsenal of weapons. He just fired thousands of rounds into a crowd from multiple stations. He also had a ton of ammo too. Pretty sure the guy is talking about the complete lack(at least so far) of political rantings, that he wasn't disconnected from society, that he didnt leave a bunch of clues, that he doesnt appear to have a record, diagnosed mental illness, etc etc. Not things that are obvious pieces of evidence right now.
Unless you have seen a report that shows authorities already had documented in advance that the guy had a cache of weapons, your point makes no sense.