I think the GP knows what cross-platform means, but is confused by using "X" as shorthand for "cross". In my opinion, it's not widespread enough for the four-letter saving to be worth the confusion.
Just to add to the different ways that that exact grouping of letters can be interpreted.
Maybe because I see an API as being able to be accessed from anywhere, so you could query it from a home automation device to trigger something when you are withing X meters of your house, which even if Apple truly released a cross-platform version of Find My that wouldn't be possible.
Xtian Xmas xfer tx/rx xor...
The argument wasn’t made out of principle, either. If it were more widespread, it would be worth the potential confusion. It’s just not. I agree with that.