i'm not sure but the fine print in the ad may have mentioned that this is for LTE/4g devices. those devices get the nfl app for free for "this season." i think they are just adding the playoffs to that.
go ahead and try it though. if it doesn't ask for payment then check it out. i have LTE but often times watch it on 3g and while it isn't great, it's at least football on my phone!!!! (wifi and 4g do seem to stream better, but 3g is definitely watchable).