ard212
It is not an IPSC rule. Some ranges, both indoor and outdoor have their own set of requirements. At the front of the rulebook that you received when you took your training course, does it state that some local rules have priority over the rulebook? If it is a range rule, that could be why the RM begrudgingly upheld the call.
I understand that it is disheartening getting DQ'd at your novice match, but as ima45dv8 stated, take your course again, and have fun.