T/O to the south is over the water, so no mountains to avoid.
They probably were waiting until the tailwind reduced to within limits (hence the sudden rush to get the cabin secure when it did happen) and they took off with a tailwind.
Often in these places you can take more weight into the air with a tailwind without mountains ahead than with a headwind with mountains ahead.
Perfectly normal procedure, and done by any airline that flies at Dalaman.