Hysterosonogram u/s dr saw a polyp. Then he & tech were discsing if it was a fibroid. Sched to remove. Is poss to not be able to difference btwn 2?

Yes. Some polyps are fibroids and are referred to as pedunculated. Some polyps are from the lining of the uterus. Fibroids are almost never cancerous other polyps may or may not be. Only way to tell the difference is to take them out and sent to the pathologist.
Yes. A fibroid under the lining of the uterus(submucosal) will look just like an endometrial polyp on many imaging studies.