What did my car just do?

During my lunch I stopped at a gas station. Turned it off, went inside, and when I came back out I tried to turn it on. However, nothing happened when I turned the key. No lights, no click, nothing. It was like the battery was completely dead.

I checked the fuses quick, and all of them looked fine. Just for grins I tried the key again, and the car started up normally (I’d almost say it was running smoother than normal). The only indication that anything was wrong was that the dashboard clock was set to 1:00, it was about 4:10 when I turned it off.

This all happened within a span of a few minutes. I didn’t even touch the battery, and even if the battery went out I’d imagine the clock would show the time it lost power as usual instead of reverting to 1:00.

I’m driving a 1990 Honda Civic DX 1.5l, if that helps.