Translation:I went down the stairs but she wasn't there.
Eh, I wouldn't say poetic. I use it in normal conversation. It is not very common, but certainly not just used in poems. The thing is, people are subconsciously making their vocabulary more efficient; If I can say "I went to the store; I went up the elevator; I went down the stairs", all using a similar structure, why use "traveled", "ascended", and "descended"?
But above all, if it's correct it should be accepted, period. You should not be graded as wrong for something you got right.