iphone 6 unlocked that was on sprint

So, I bought my iPhone 6, gold, 64gb, sprint, from eBay, brand new in box- sealed 2-3 weeks after the release. I chatted with a Sprint representative about getting it unlocked domestic and internationally, she said she did it through her system, I followed the instructions which were to backup the phone, reset it completely, and restore it. So after I backed up the iPhone 6, and erased it, I got a confirmation on the iTunes windows that said, your phone has now been unlocked. I took it to a AT&T store and the guy popped his sim in their and it worked, data/voice with no issue and I couldn't be happier. My question is: if i ever reset everything or do a apple iOS update will that void the unlocked and the phone would be back on sprint; another question: so sprint unlocking my iPhone, does that mean it's factory unlocked now?