Uh huh. So someone posts an 81 byte op return. Core validates the block. Knots does not validate the block. There are now 2 chains. Those 2 chains can never merge or reconcile. That's not a hard fork?
nope, not a hardfork. bip110 uses existing consensus rules rather than adding new ones making it compatible with all nodes on the network
nodes that enforce bip110 would not ever see the offending block as valid, making the enforcing node only ever compatible with one side of the chainsplit.
nodes that dont enforce bip110 remain compatible with both , but only one side of the chainsplit carrying perpetual wipeout risk. both sides of the chainsplit ultimately cant coexist without a hard fork present
a hardfork would explicitly reject bip110 blocks which would be adding a rule.
nodes that enforce bip110 would not ever see the offending block as valid, making the enforcing node only ever compatible with one side of the chainsplit.
nodes that dont enforce bip110 remain compatible with both , but only one side of the chainsplit carrying perpetual wipeout risk. both sides of the chainsplit ultimately cant coexist without a hard fork present
a hardfork would explicitly reject bip110 blocks which would be adding a rule.