Whoa.
When the mind and body don't quite sync this can happen. I think he did imagine it to be going to his FH, I guess from looking at the toss, his peripheral vision told him it was going to his BH but he had already anticipated it to be closer to the middle of the service box. Thus he already commited hitting the return as a FH and in the middle tried to adjust by running around it, but you only have so much time to do so (I think even if he changed midway from FH to BH through his stroke, he still would have missed). Ended up being a rather big ROS fail and an unlikely ace.