That sounds like an interesting story. Do you have any further info about Apple using a Cray for prototyping?
There is an often cited quote from Seymour Cray when asked about Apple using Cray computers to design the next Apple: "That's interesting, because I'm designing the next Cray with an Apple!"
Some people take this seriously, not realizing that Seymour was being sarcastic. He used pencil and paper to design his computers, not even an Apple II.
Thermal design, fluid dynamics. Apple said as much in advertising at the time, IIRC
Interestingly enough, Jean-Louis Gassée briefly mentions something about using a Cray to develop what was to be an Apple-designed processor decades before it was fully realized https://mondaynote.com/joining-apple-40-years-ago-805114536a... (See a little more than halfway through the article)
For those interested in the details of the cancelled Apple processor, here is the manual: