An AMP is a page (expand the acronym). I answered your question very precisely, and your response shows that you still don't understand it.

> If I'm using magic words correctly, I guess what I want to ask is what percentage of AMP traffic to cached pages is served to users by Bing and others that aren't Google.

If I search on Bing, the results will be prerendered from Bing's AMP cache. Reread the GP comment, and see if you can understand why that is so.