That can't possibly be the reason. Upgraded nodes would never validate blocks mined by the old nodes!
So no matter what old nodes do, they would stay on the old chain and not interfere with the new chain.
The problem was rather that the new nodes never forked, i.e. there was never a new chain.
Something went wrong with the upgraded nodes and it has nothing to do with the old nodes.
If one old node could prevent an HF from happening then there would not be any HFs anywhere on any chain
I know why I didn't delete my VM with the old wallet yet