I'll give the same answer they will for every X-Men movie going forward.
Don't Worry About It
I can understand some denial here, no fan of the X-movie verse wants to see everyone get screwed over in the end. Still....these fox X-Men movies do try to retain continuity with eachother.
If this takes place after the happy ending timeline we got at the end of DOFP? Then it kinda makes preventing the DOFP timeline not as satisfying, when you consider everyone still met with a bleak fate and died horribly in the end anyway. WTF.
I don't know who caught it worse, Professor X or Wolverine....
Still a great movie though.