I think they are practising a bunch technique.
DH was competing in a 160km cycle challenge and riding in a large bunch. He saw a guy have a front tyre blow out on a downhill (he heard the tube go) and the two guys on either side the rider grabbed an arm each and helped him slow down to the side of the road.
Also bunch ridiers "help" each other ie if they need to adjust a shoe or something on the bike by holding the person up a bit.