Your speculations are right on.
The gut says be suspicious.
At the time, I saw several twitter reports of people saying they heard 2 shots. Checking data still in my RSS feed maybe this is what I recall. … (pics)
So it was the OANN cameraman who reported hearing 2 shots.
There are a lot of contemporaneous news articles and it's hard to say which are authoritative. Fox, TheHill, etc. all had something right after it happened on Saturday March 3rd.