Car trouble

I had brakes repaired and a oil change the car was
left jacked up overnight the next day when the work
was finished the car started right up  but when
pushing the gas pedal the car would not move I
could go into reverse neutral and drive but when
pressing the gas it would not it would just run them
up high  No the guy that fixed the brakes and
change the oil told me to check the transmission
fluid and if it was low to fill it then it would be fine  
he says that from having the car jacked up for so
long that the transmission fluid leak to the back of
the pan and that it would just need to be filled them
will be fine is this true?