I noticed it Wednesday, not so much boos which as you say i think were aimed at the ref, but lots more groans and moans when a pass went astray, i had a chap near me who nearly popped a vessel, you could see the veins on his temples throbbing.
This is an interesting concept and i wonder if i drove a Russian tank to the Polish border and crossed half way over so the gun was in Poland but not the back end, would N.A.T.O take that as an invasion of Poland or not.