I don't believe him.
Also, they've been building up Banner/Hulk's character in Ultron where he's still going on the run and I'm sure they won't go the same route as the Avengers 1 or Incredbile Hulk where he's hiding in Brazil or India. It's too redundant.
Also, having Hulk as a supporting role would make sense since he's the hardest out of all those heroes to do a stand-alone film for.
I dunno. It's such a perfect storm of story elements and beats that fits into the entire saga. It all comes full circle with a reason for the Guardians to go back to earth. They stumble upon Hulk in the colloseum, they might be prisonners there, they need Hulk's help (he comes from earth as does Star-Lord so there's a connection). If he helps them, they have to bring him back to earth in return and he might drop some Infinity Stones knowledge on them in order to motivate them to also go to earth.