It is definitely HS-on. The only question is if it will start in July or September.
They likely reprinted HG/SS cards for one of two reasons: They didn't want certain older cards to be legal for longer than they needed to be (yeah, sure, a couple of cards like Warp Point wouldn't break anything, but it's still not a great idea), or they plan to make the next rotation (after HS-on) CL-on. Either way, don't look too much into reprint sets. They don't often reintroduce older cards, especially not Trainers/Supporters/Stadiums. And even when they do, they only do it from within the same era. (Power Keepers reprinted numerous cards from the EX series, for example, just as Call of Legends did for HS.) Legendary Collection may be an exception to that, but meh.