My girl is bell trained and it's great, otherwise she just stand at the door. My old girl used to bark.
This is one of those thing that can be normal or not. If you have several of these incidences, it doesn't hurt to have a urinalysis run. When my dog was having occassional accidents, I thought it was a housetraining issue, and it wasn't - she had remnant tissue in her vagina which was causing problems - it showed up as high white blood cells in her urine. Could alo be a uti.
If it continues, i would rather have a urinalysis run and find it's completely normal, than to not have it run and miss something.