Toyota Prius: Question Prius tran. drain and flush

Yesterday while driving my 2004 Prius on the Avenue of the Saints
(near Iowa City, Iowa) at around 70 mph, the black plastic splash pan
that covers the underside of the car (pan is around 8 or 10 inches
from front to back and the width of the car - attaches in the front to
the bottom of the front bumper and in the rear to some brackets
slightly behind the bottom of the radiator and fan shroud)
disconnected from the front bumper and began dragging on the roadway
(made quite a racket). I immediately pulled off the highway and
crawled under the car to see what damage had been done.

Thankfully no serious damage was observed and I was able, after
considerable effort, to re-attach the pan to the proper connectors and
get back on the road. But, there may be some history here that needs
to be addressed at my dealers shop with their Prius tech.

I recently had this car in for service. The tech informed me that the
transmission was due for a drain and flush. I told him to proceed with
the needed service.

My question is this...is the splash pan removed or loosened when
draining and flushing the transmission? The screws that are intended
to attach the pan to the front bumper were backed out all the way and
I just cannot believe that they all vibrated loose the same amount -
seems like more than normal vibration loosening to me but I am not a
mechanic.

Thing is, if the tech accidently left the screws loose I want to
discreetly tell him about his mistake. I don't want him to get into
trouble. He's a very nice young man and has been very helpful to me. I
want that relationship to continue and, plus, he's a devoted Prius
driver himself. Truth is though, if he made a mistake he would
probably want to know about it...I certainly would.

Thanks for any info...

Got one of those "hope you're Completely Satisfied With Our Service"
form letters from my dealer relative to the recent service they
performed on my Prius. I thought that was pretty timely so I called
the service manager and told him my story. His reply was, essentially,
"sounds like it may very well have been our fault and it will be fixed
at your convenience".

So, hopefully this will end my little frustration.

Thanks for the replys.