It raises a lot of questions. Why is he the only source? No official notices, from FAA or airlines or pilot unions, have mentioned this. What was the cause of MCAS activation? Did it activate for it's intended function, or because of some malfunction? Why have none of these pilots spoken out? Why has Boeing not said, "See, pilots can do this!"? Why hasn't someone else said, "See, it malfunctions all the time!"?
I would say, generously, that this is very unlikely to be true.