Why is that any more excusable? Whenever I've been prescribed pain killers, benzos or other meds not safe to drive on, my doc has made that fact very clear, as has the bottle they were in.
The difference is likely you are more aware of how fucked up you are with alcohol. The effects can be a lot easier to understand. I say that because if you have never mixed pills before, you may not feel it the same way as you do with alcohol.
Plus, with alcohol involved, it sounds more on purpose than his excuse does.
He may be telling truth or it may be bs...whatever the case is, he could have hurt someone else while being under the influence of something, so he's wrong.