Depends on the State, but yes: It´s way to easy to get a Gun overall. But that won´t change in the US. Way too much Money on the Line.
There is no Culture in the US other than Outrage Culture.
- - - Updated - - -
Not irrelevant in that Case, because he was an Attendee at the Tournament. As far as is known right now he played, lost and started shooting (Simplified).
That means he brought the Gun in before the Tournament even started. Which implies a Lack in Security, and that puts Blame on the Organizers.