Not sure what they mean by "mysterious". He isn't hiding and never was. He posted his photo, name and other personal details in articles about MikroTik on Russian IT blogging platform[1]. His name is Alexey Sopov, 34, from Novosibirsk. Quick search revealed his social network accounts:
Is there a way to opt-out or disable this telemetry? Under privacy laws isn't Vivaldi supposed to give users a choice: whether they want to be tracked or not?
https://fb.com/100005153643926
https://vk.com/lmonoceros
[1] https://habr.com/post/353530/