Speculation? Yep. But it's reasonable they're not going to put much effort into looking for 1mpg....maybe check for codes & call it a day.Uncalled for speculation presented as fact (unless you are the actual mechanic (not) doing the work).
The dealer should be checking the fuel-air ratios with a scan tool to see if an unusual amount of correction is needed to get to the proper ratio, possibly signifying leaking injectors and reduced fuel mileage.
Uncalled for? Can't say but I'm glad your here to be the arbiter of opinions.