While Apple probably didn't help Intel design the Core 2 Duo (they only had serious in-house processor design stuff recently, and it's ARM-oriented), it's quite possible they exerted pressure on them to make such a thing. The Core Duo and Core 2 Duo were a _major_ turnaround for Intel; they essentially abandoned the gigahertz at whatever price doctrine they'd been pursuing since the P4.

The Core Duo, in particular, was essentially _only_ found in Macs; it had very limited deployment elsewhere. It fits very well with the circumstances of the Intel switchover; Apple couldn't have used the P4M for its laptops (far too power-hungry vs the G4), or the PM (barely faster than the G4 at all, used somewhat more power).