This has been happening for at least a year, probably more. I always assumed it was something the creator had to manually mark, never considered that it might be automatic.
(I use the VTT on my Firefox, I use IDM to download the auto-generated English language scripts for lengthy videos).
I remember listening to Chomsky saying that he prefers to read the transcripts than listening/watching speeches.
It is one of those things I don't care (at all) to know how it is technically set up :)