The only reason I can see this happening is if Hexmag specifically did not brand these magazines as "Pistol magazines".
As arbitrary as that is, it is the requirement for the "designed and manufactured" clause of the firearms act that makes pistol magazines not prohibited.
If IRG thought they could import 10 round mags and declare themselves that they were pistol mags, then they do not understand the firearms act. This would be their own fault.
If these were in fact "designed and manufactured" for use in a pistol, and the RCMP is declaring that the method of restricting capacity is insufficient, then a rivet would remedy the situation, just like any other pinned 10/15, 10/20, 10/33 glock magazine.
If that is still not sufficient for the RCMP, then this issue is unprecedented and we have a real problem on our hands.