I really don’t see how this feefilter logic works, how does 10 relate to 0.1 sat/byte and how is it 81 less restrictive than 10.

Looks like that was indeed a mistake, setting it to 81 was already flagging the peer to be evicted, but there was a race between that and the test check: https://github.com/bitcoin/bitcoin/pull/28488#discussion_r1357082117