Well practically speaking it only applies if there is something the EU can do about it and if you're doing business in the EU they certainly can do something. Even FB, for example, needs to conform otherwise all that ad revenue from EU companies can vanish if the EU governing bodies sees fit to do so.
But the most the EU could do about the Arc forum would be to block EU users from accessing the site (which would be a political nightmare for them in censorship terms). And, in reality, this site doesn't hold any real data worth worrying about and I somehow doubt PG is sitting around worried about what the EU thinks (regarding this site).
None of this has anything to do with what I think of the laws they are creating. Frankly from the little that I've read I kinda like what I see, but still the world doesn't abide by whatever the EU says, as a parallel example... just look at how much trump cares about nafta right now and that's an agreement they signed. (I'm Canadian btw).