If its supposed to be ERW ( ?? ) MS then look for the weld seem, DOM wont have that though. You could have it sonic checked or weigh it and compare the weight to another known MS Chassis.
If it is the same thickness as MS and painted, I dont know how to tell w/o causing at least a small amount of damage ...
If its not painted you can look for the grade markings on it ...
If this guy is just whoopin up on everyone else ... it could very well just be he is a better driver. Have a friend who went through that, won the Season Points his first year and missed the last 3 races ... he just out drove everyone .. regardless of who's cart he was in.