I don't think it's been mentioned before.
Had to scroll through the sea of comments that were praising him to find the comments you're referring to, but some comments did mention how Filip might have taken inspiration from another YouTuber called Nihongo Gamer, to which Filip himself claimed that he only saw after he finished filming his own video.
Of course, by now I don't think everyone would believe that. However, someone should go compare the two videos and see if this is yet another case of plagiarism.
Filip's Video:
https://m.youtube.com/watch?feature=youtu.be&v=Iih31oSyX-8