I commend you for giving this topic such a thorough review. When I was Pentecostal/ charismatic, I “received the gift of the Holy Ghost with the evidence of speaking in other tongues.” I saw it happen to other people, but I’m convinced now it was all gibberish, myself included. I never saw anyone speak a real language that was foreign to them. What your friend did seems extremely rare. I can only conclude there is real Acts 2 speaking in tongues, and there is gibberish people are pressured to believe is tongues. Since we have such a small sample size of the former, like you, I can only call it a mystery.