Hi Frank
Though you should've been more careful with cleaning your scope's mirror, the fact that there was a lot of moisture in the air the night you looked through the scope, meant it was probably warm air just over your mirror causing the poor seeing. The reason why the moisture was there was because the evening cooled rapidly from a relatively hot day, plus the humidity would've been fairly high. Your mirror won't cool as fast as the air, so the boundary layer just above the mirror would actually be warmer than the surrounding air. The fact you never had your mirror fan running would most certainly make a difference. No airflow over the mirror would've prevented it from cooling rapidly enough to equilibrate with the surrounding air, plus it would prevent that boundary layer from dispersing.
Next time you go out observing, turn the mirror fan on for awhile and then check it through an ep on an object. I'll be pretty certain you'll notice the difference