Here is a thread from 7 months ago where more people noticed the video was plagiarized due to a DMCA of a re-upload: https://www.reddit.com/r/youtubedrama/comments/1391d4o/internet_historians_man_in_cave_video_was/
But to actually answer your question, it takes time to prove (or even notice) when a work has been plagiarized, particularly when the person who did wrong does not mention, or intentionally hides the original source. The Hbomberguy video is about exploring that in depth and the IH video is just one example, not the main topic.
Every day, I have an app that connects the audio of my pc to my phone through wifi and using bluetooth would just make the whole setup unusable for calls + wifi has better range and audio quality than bluetooth. The whole setup is PC->Ethernet->Router->wifi->Phone for ~30 ms of latency and the app is soundwire.