Who knows? Every dude is a story for himself. Some guys DO mind. The others could not care less. And quite a few are somewhere in-between...
A few str8 men find f2f sex very arousing. Since no male is involved, they reason that there is no cheating either. Besides, there will be no offspring to rear after such an encounter, so why worry?
Human sexuality is still mostly viewed from the phallocentric perspective even these days. Hence, among many str8 males, f2f sex really doesn't count. On the other hand, m2m sex matters very much from the same point of view. Men very usually police their sexuality and are far more restrained when it comes to, say, PDA as opposed to their female counterparts.
There is yet another aspect of this specific video worth mentioning. The women shown are by no means your stereotypical lesbians who may somehow be perceived as questioning the existing societal order by their attitude. These two may be lusting for each other but if anything ever happens it will stay a private affair!