The fact that you did not hear WSM on a second day would indicate it was skywave. Groundwave is constant, so if it were ground wave is would always be there (unless knocked out by someone else's skywave.) Nothing uncommon about occasional midday skywave in winter, but the lack of higher frequencies is interesting. You were tuned to the right place at the right time.
Are you the same DXer who said on another message board that they had a problem with interference from WDFN to WBBR on 1130 during Critical Hours in Poughkeepsie?