It didn't ban nodes.  That instruction simply installed an ETC client or an ETH client.   With a different protocol.  It is as if you could use a bitcoin core client, and give the instruction --run-litecoin.

And transactions from one chain WERE transmitted to the other chain, which caused a lot of surprise.  But this is normal: miners wanted the fees, so they went LOOKING AFTER valid transactions (not on the network, but on the block chain !).