Yep. Armed and uniformed soldiers crossed a border between them and a state they are currently at war with. That is an invasion. A particularly shitty one, but what else do you expect, it's north korea, they've been incompetent since day one. Even during the korean war they needed the Chinese to do the heavy lifting.
If you don't think that is an attack, then the US has never attacked anyone. Vietnam, Iraq, Afghanistan, Korean, Iraq again, whatever. Those armed and uniformed US soldiers probably just got lost on the way to the bathroom. Ya know, you're at a party at a new house, you've had some drinks, it's two doors over and to the right, but you turn left and accidentally topple a socialist government lol. Just a warning shot. S'all good.
Edit: actually, the sheer incompetence explains why NK thought working with Russia to fight in Ukraine would teach them some good invasion lessons.