Please don't ask him this question again. If the car stinks, you know the answer - no need to ask. If the car does not stink, then the question is not needed. There is no new information you can draw out of him by asking - the smell of the car tells you everything already. Since your husband feels guilty, and since he is in the habit of hiding smoking anyway, that question was like testing whether he'd lie... you put him in position of a schoolboy who is hiding his pranks or cheat sheets from his teacher. It was as if you had a huge pile of very dry hay and one lit matchstick was enough to set it ablaze. The pile was huge and very dry from infidelity and the matchstick was the question about smoking. The situation is so volatile that avoiding such touchy subjects for awhile would be best. Also, he most likely lied to you on autopilot - since he was in the habit of HIDING his smoking, as you wrote, his default setting was not telling the truth (hiding is similar to not telling the truth).

There is nothing you did wrong, but if you can avoid this issue in the NEAR future, that would be best. Once the dust settles, the issue of smoking can be revisited, but right now is an awfully bad time to talk about smoking.

That you had a good scream is good - hopefully it was cathartic for you and him. Don't view screaming as a failure - the steam had to find a way out.