I'm not sure I remember the part where Indy is buried chest deep in sand with one fist defiantly raised ... It looks more like a character model glitched under the map!
I think OPs point is that if Indy was burrowing a hole in the desert, and some random started talking to him, Indy probably wouldn't respond by punching his way out of the hole.
Because he is. The person he is speaking to is a Nazi. there are other Nazis behind him. They probably dug a hole a left him there to die or something (we lack context for the scene, but it's believable). Full scene: https://www.youtube.com/watch?v=0e17p2IVDUU