I have recently heard a lot of people (most of whom have learned English as a second language) use the phrase "I slept at 9 o'clock" instead of "I went to bed at 9 o'clock" or "I fell asleep at 9". I was wondering if there was any idea as to the origin of this phrase.
It doesn't sound at all odd to me.
At seven I ate dinner, and at nine I slept.
While laughably untrue, this is grammatically correct, and the sense is clear. If you look at the native language of a non-English speaker who says it this way, you'll probably find that the typical way of expressing the sense is I slept rather than I fell asleep or I went to bed, that's all. (I know this to be the case in Chinese, for example.)