AMD being a “partner” is business speak for “AMD paid us a bunch of money because having their brand on our product is a much larger advertising reach than they can accomplish on their own”.
That performance is better on AMD is in no way “bizarre”… it’s exactly what would be expected.
Bribery?
Every time you start a game and see an Intel, AMD, Nvidia or other logo outside of the studio or publisher, that’s paid advertising, plain and simple.