QA testing is a part of development, but the QA testers are not developing, therefore not developers if that is their only role. In some companies, generally smaller ones, developers are the ones who do QA. In other cases, QA testers will often become developers because knowing how to develop does help to better know what to test. And since developer pay is generally better, they transition to that full time. Saying that QA testers are developer is akin to saying managers are inherently developers, since management is part of the developer process. While managers at game dev companies should be former developers, it's not always, and nowadays even normally, the case. All that said, he is right that the perception of QA is toxic. They are generally perceived as less important and less intelligent, while being an integral part of releasing a good product. It's kind of like with SKG. He uses like one or two true/good points, then tries use those points to try to paint the whole thing as shit, despite it not being related to the issue-at-hand.
It's funny that he still has this cloak of insecurity around his QA position at Blizzard. The guy is a rather successful streamer, and he has shown that he has the knowledge to develop a game (whether it's good or not is not really important in this case). He should just ignore people point out he was a QA guy at Blizzard. Just like the best course of action would have been for him to ignore the SKG drama after he ran his mouth too much. But he can't because he is cripplingly narcissistic.