I can only think of 5 reasons why an amateur pilot or a non-drone person who made this statement and I'm not an expert in this but some variation of:
1. If the drone was flying high and far away and it flew so far that it disconnected and the setting was Hover, it the pilot doesn't understand what is happening thinking they can still see the camera view but the drone won't move then it's stalled.....or,
2.If the maximum height is set to 400 feet and you start flying far away and you try to go to 500 feet and but you hit that ceiling at 400 feet and it won't go any higher but you really need to get the drone up and over, the drone might appear to be stalling if you don't know there is a manual setting....or,
3.If you are running a mission (that you didn't set up) and along the way the drone lose the connection and the setting is to Pause or Hover, the drone will "stall" along the route and since you are disconnected.....or,
4.If there is some weird geozone in the drone's software or you are running a rogue drone program and you leave that zone and now you can't get back in from some reason, the drone appears to "stall".....or,
5.What I is believe which is dishonest, deception, and disingenuous on the part of the city and the drone organization, and all the actors involved. No transparency, no accountability. Not saying there is ill-intent from the beginning, this isn't a false flag but they appear to be covering their tracks or failure to admit fault or not making it seem like they jumped to conclusions.
IMHO