It sounds like the fellow may have been breaking one of the cardinal rules of muzzle loading. In order to use his dipper, was he dipping into an open container of powder which is a big no-no? There shouldn't be any open containers of powder at the range or firing line. All the containers are supposed to have a pour spout with a cover attached that should be closed immediately after pouring it into a flask. Then the powder in the flask is poured into whatever he's using as a measure.
I don't know if he was using a sub. powder or not, but he would get warned if he was dipping into an open container at my old BP club. Unless he was pouring it into his dipper and that was omitted from the scenario described.
When I pour into my measure, I do it over a plastic box to catch any spillage, and then I use it up before much accumulates.
But having any open container of powder near the firing line is a red flag. If someone's alone then they get away with doing it, but when others are shooting, hot cinders can be in the air which make any open powder a hazard. Buying a pour spout was something I was once warned about when I was a greenhorn, and I only poured from my container to fill up my flask, so that's why I remember about that rule. Especially the old timers, they really don't like to see any open containers.
It was because of all of their years of experience I guess.