They knew the flowmeter was off by 10% and asked all the teams to adjust to that number, RBR thought they could get around it by using their own measuring method (iirc it was a lot closer to the engine itself, maybe the injector) that they claimed (and are able to prove) is more accurate. So that's the sticking point, the fact that they went against a direct order they easily could've avoided. And as @
SVT Cobra GT said, they were warned and still went on as they did.
Shows to me that they had this shady business planned out in advance and it's really crappy of them to do and try to defend like they hold some special place above the other teams or the other teams just aren't clever or brave enough to use the FIA's incompetence against them