As an update to the story, this was confirmed by Gabe himself: https://www.dexerto.com/entertainment/gabe-newell-responds-to-fan-asking-about-bizarre-valve-throat-singing-story-3412684/
A fan then went straight to the source, emailing Newell to ask whether the story was real. In a reply shared online, sent from Newell’s Valve address, he provided more detail.
“Yeah, I had chatted with Paul Pena about it after I tried learning on my own,” he wrote. “I am entirely self taught and it shows.”
He added that he worked on the sygyt and kargyraa styles “and got to the point where I was really… annoying.”
Newell says he still hasn’t given it up entirely. “Every once in a while, I’ll pick it back up,” he wrote, adding that it takes a couple of weeks to condition his throat.
Pena was an American blues musician who taught himself Tuvan throat singing, later becoming the subject of the Oscar-nominated documentary Genghis Blues.
And what about reconning the ending to episode 2? I already explained that I didn’t fine the gameplay of HL2 to be very good, so if I played it through for the story, why would I be happy about that? I stopped expecting to get what I want out of a Half Life game when Marc Laidlaw explained the circumstance of why he left.