I saw it live. The serve was definitely not returnable from his back hand. I think By the time he touched the ball, the wrong call also came at almost the same time.
Well to blame this on top 4 is totally uncalled for. Get better Tsonga if you want to beat them. Not cry on a line call which you would have not returned anyway.
I have seen even Nadal on the receiving end of such calls, so it happens to every one.