The question is, how much room did the AV have in front of the bus to merge out in front of it?

I'm wondering if the bus was cruising along and saw the AV inching out into its lane and just thought "Oh, once they see this big-ass bus coming along, they'll stop trying to merge." And the AV thought "Once that bus sees me inching out, it'll slow to let me merge." And neither one was right.