JJ talked in an interview about how fun it was to work with Ian.
I must of missed that but bear in mind JJ has lyed in the past about his films take his Khan quote for example.
JJ lied in that case so as to not spoil a reveal. I can’t imagine a reason he would outright state he worked with an actor if that was not the case, and why everyone involved in the film would say he’s back if that’s not true. If anything it seems more like Ian is the one playing coy here, probably trying not to give anything away about the nature of his role.