This is EXACTLY my thought process. If the cook in a food truck has a respiratory infection, and he serves 100-200 people per day, just imagine 15% of those people get the infection; that's 15-30 people. But chances are it would be A LOT of people infected.
And I am not a virologist but if the truck is relatively small and the cook has it, the viral load in that truck would seem to be high.