Misleading title. This was not a bug in Ethereum, but in the code for a particular popular multi-sig wallet people use on Ethereum. I don't mean to trivialize it, but this is kind of like saying "Bitcoin was hacked" when MtGox went down.
OTOH, Ethereum really encourages these types of bugs due to how it's setup.
These types of bugs are characteristic to things written in Solidity. So no, Ethereum didn't have a bug, it just encourages buggy programs, and this is great example.