Ah yeah, I boxed the player in on start of the boss fight on this build of the game . I've changed it so that box is removed on the upcoming build, but of course I can't upload it yet due to the restrictions.
When I was building it, I wasn't sure what I was thinking, since I could just adjust the trigger to fire on exit instead of forcing the player to walk forward, and I do think that's caused some confusion for players. With the next build, that's how it works - the fight will start no matter what direction you walk once you leave the spawn area.
But its already fixed, just suck in limbo for now, sorry about that!