No, they would have been alerted by lack of radio communication if they had a wrong frequency and had been awake.
Air planes fly in and out of various frequency sectors. Simple inattentiveness can lead to prolonged periods of non-radio contact.
The radios never really go silent, as there will almost always be some frequency chatter heard from other vicinity aircraft, even when out of range of the ATC transmitter, due to the extended line-of-sight maintained between high altitude aircraft.
Once it is realized that radio contact with ATC has been lost, finding a frequency that works for the existing location takes some research. Modern airliners do not monitor “guard” frequency the way military aircraft do.
Often times, ATC will call the airline dispatch to get an ACARS message (called SELCAL) to the crew to alert them to the problem.
This is not a totally isolated occurrance. But when coupled with an improperly set up FMC, it can lead to major embarrassment and loss of safety margin.
I really doubt the “asleep” assumption.