So you’re watching a sitcom or something on TV, and suddenly the station decides you need to be reminded that a different show will be coming on later. So they run a little silent commercial at the bottom of the screen, with the name of the show and a couple of cast members smiling and sometimes waving at you.
I seem to remember when they started putting a small logo for the broadcasting station in the lower right corner of the screen that they were officially known as “bugs”. A friend used to complain about them as an unwarranted intrusion on his viewing. I’m afraid to think about what he would say about the current pop-ups which take up so much of the bottom of the screen. There have been times when they’ve actually covered up things relevant to the plot of the show.
A union print shop will include the logo of the printer’s union somewhere on all their work. That’s the “union bug”. I don’t know whether that’s the origin of the term “bug” as applied to vid, but it’s been around since the heyday of the union movement after WW-I.