You are correct. It wasn't a hard fork, but that is not really the point.
The claim is that Bitcoin and Ethereum are different because Bitcoin transactions would never be undone in order to fix something that people feel is an exploit. Yet, it has been done.
A 51% attack against Bitcoin was successfully executed with a client that enforced new consensus rules in order to undo transactions that were valid under the current consensus rules.
You feel that there was a "bug" in the consensus rules that needed to be fixed, just as people now feel that there is a bug in the DAO contract that needs to be fixed. It all looks the same to me.