These comments are very familiar! We, too, would explain that we did not celebrate Thanksgiving because "we are thankful every day." And my mother would do a full Thanksgiving dinner. I mean everything! Whole turkey that was roasting all day, mashed potatoes, cranberry sauce... all of it. She, too, would claim that the foods were all on sale and it made the most sense to buy these items.
(Now, I'm sure that the turkeys were much cheaper around this time, so her rationale wasn't crazy. But the other trimmings? The mashed potatoes? The cranberry sauce? Maybe the prices were slightly lower to move the extra inventory (though not at first) but I can say for certain that the only time we ate cranberry sauce was at Thanksgiving. It was a very specific purchase.)
It was only for us (her and her children, and maybe my dad, if he managed to show up). I do wonder if there would have been any issues if the elders had gotten wind of it. My mom has always been a 100% die-hard JW, and I think that she would have been mortified if anyone in the congregation had seen the spread she laid out each year.