dro = hydroponically grown
It doesn't indicate quality, it only establishes that it was probably a well-tended plant since there were relative laboratory conditions involved. It's a really stupid term for weed, but that sorta goes with the territory.
At least you can assume it wasn't grown in a ditch, but that is pretty much all that anyone is going to know about your particular batch, short of smoking it themselves.
There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.