It is possible, but unlikely, unless this was the only car they had in to work on.
As there is a corrosion question/issue, as well as other safety issues, I would just have a look yourself to see if there is any new metal been welded in, you will easily see the new patch with fresh underseal on it.
My suspicion is it's a dud MOT, if there are signs of holes/corrosion on the sill as marked I would be very concerned, these bits are normally marked in yellow marker.
If it transpires that it still has any of these faults I would be straight on the phone to VOSA, or the MOT inspectorate, as cowboys get the decent honest guy a bad name, and cowboys need to lose their license to do mot's.
Like I say though, if they had enough time it could defo be done in a day, maybe they are a genuine helpful garage, but looking will soon tell you, or if not confident get another garage/mate to have a quick look.
tabetha