My apology, I think Dove's explanation is the correct one.
I've searched and found that they don't factor the previous performance of a neighborhood anymore for derby matchmaking. But that you will be competing against other Neighborhoods of the same size at the same league. The rest is random I think.
Here is the link I found for derby matchmaking explanation:
https://supercell.helpshift.com/a/hay-day/?s=neighbourhoods-derby&f=derby-matchmaking-after-leagues&p=ios