That's where I'm stumped- it's a flange head bolt that's isn't stuck at the head, and I can't see how anything could be holding on at this point. I'd be less confused if I hadn't already done the passenger side. There is maybe a 2 paper sheet thick space around the head if I wiggle the bolt, but somehow I can support a good amount of weight when I lift into the bottom.
This is the bolt with the trouble spot marked.