Should you freeze pastry lukewarm? If so, why?
I think it's because freezing tend to dry things out. At lukewarm temperature, it's still 'steaming' a bit, which means evaporating liquid, so losing moist. If you can stop the drying out process at that point, the pastry won't be as dry as when you let it cool completely.
Of course, a too high temperature can do harm to already frozen things, or would cause condensation in the package, so that there would be ice formed.

This could be the reason, and therefore, the statement can be true.