There are couple things going on. Your sense of smell gets desensitized to the smoke from repeated/long-term exposure, so the smoke flavor doesn't taste as strong and may seem a bit off if eaten the day of the smoke. Add to that, your clothes, hands, hair and everything else exposed to the smoke is carried around with you all day until you remove it and take a shower, so you really can't escape the smoke by just walking away from the rig...it escalates the desensitization quite a bit. While refrigerated, the smoke can equalize/penetrate deeper into the food, giving a mellower but deeper flavor. I've aged smoked potatoes for a few days, and yes, you can definitely tell the difference...much, much deeper smoke with a better overall flavor than straight off the grates. Cheese is the same...smoke it, then age it...far superior to freshly smoked.
If they seemed more tender, that can be effected by conditions during cooking, storage and reheating, but specifically for this discussion: how fast and by what method, humidity present in the cooker, actual internal temp when reheated, etc. If they were cooked to med/rare, they should have been quite moist (again, depending on methods for cooking), then when reheated to a safe internal temp of 165* (for leftovers), if a good method for reheat was used most (not all) of the interior moisture should have remained. Moisture can directly contribute to tenderness, in a roundabout way...drier will become more of a chewy texture.
That said, whatever you did for cooking, storage and reheating could be duplicated, if you liked it...hopefully you recorded pertinent info or can remember it to do so now.
Just so you know: http://www.foodsafety.gov/keep/charts/storagetimes
Enjoy the smoke!!!