First of all, tobiano does not exist in Quarter Horses and never will.
Quarter Horses are descended from breeding shorter, stockier Thoroughbreds. Paint Horses are descended from spotted horses brought over by the Spanish, then bred with TBs and, yes, QHs.
The two breeds (along with Thoroughbreds/JC) are so intermingled that distinguishing the two can be difficult, but yes, they are all 3 different breeds. Many APHA horses are entirely QH due to the AQHA's old rule about excessive white. The APHA eventually did put a stop to it and required that to be registered APHA, there must be at least one APHA parent.
Since the excessive white rule has been repealed, you can also take your APHA registered horse and get full AQHA papers for it too, which leads to APHA/AQHA horses.
Lots of confusion..but I hope that helps.