The knife being legal or illegal is of no consequence to me. The fact is - He had a WEAPON.
Why is the knife being legal or illegal of no consequence? If it was legal (and I'm not saying it was - it certainly looks like it was not), then who cares if he had a weapon?
So what? Most commenters on this site probably have WEAPONS.
Maybe he was going fishing and uses it to cut bait, or maybe he uses it to cut kindling for his campfire. Or, maybe he uses it to mug little old ladies.