I doubt it, given that no one automatically gets Freedom Awards. (You have to convert two Standard Awards.)

But it could have been due to another anomaly: Southwest doesn't open their schedule anywhere near the 10 to 11 months that other carriers do. So if the booking window was near the Southwest schedule-opening window (which would be a less-than-optimum time to look for awards on carriers which open up 10 or 11 months ahead), then the 99.3% number could have been in large part because they have many dates for most destinations right after they open a new section of their schedule. (Their schedule is opened in "burst", as the threads constantly asking or mentioning another schedule extension in the Southwest forum attest, as opposed to the majors where it's more or less daily a certain number of 300+ days out.)

Another factor: Southwest flies point-to-point, not through hubs, and has many (although some very inefficient) connections for most city pairs, and the initial award availability calendar shows whether any conneciton is available that day. If that's as far as they looked, Southwest would have come up with a great score. My beef about it is that much of the time when you click to expand that to show the actual award flights available, it's some awful time (or awful roundabout connection) that I don't want to take.

(Of course, I've also had the same issue with AA and UA sometimes, with them only finding me redeyes on eastbound transcons. But that issue would go away if the study didn't search eastbound transcons!)

So it makes a huge diffeence whether they just gave dates and accepted any time of day and any routing on the flight, or if they had a time window and a total flight duration limit...