RADIOs FOR USE IN SIV ALWAYS?

hi i have watched a student siv training in oludeniz.over the water .and the student was trying to do a stall.i couldnt see any radio .what so ever.anyway the stall went wrong.he let go of the risers.the risers got tangled.and then the student had to use hes reserve.he crashed into the water.and was floating.even at this time i never heard the student on the radio at all...calling for help...i need help.if any type of training is going on do students have another way of communicating to a instructor? or this video the student just didnt bother useing a radio at all.please comfirm.ill try and find the video.with no radio that i couldnt see at all. the student is a student and he is no expert.