TorrentFreak broke the story, and it's not surprising considering Nintendo's reputation for taking emulators and fan games using its intellectual property out of play. Considering you can purchase Game Boy Advance games on the Wii U, a route that still monetises for Nintendo, its not difficult to see why they took the step.
However, as the Switch doesn't have a Virtual Console, the only way to play Nintendo's back catalogue seems to be the Wii U or 3DS virtual consoles, currently. Only the Wii U currently supports Game Boy Advance titles, unless you were fortunate enough to be part of the Nintendo 3DS' ambassador program.
While Nintendo can play whack-a-mole with unlicensed emulators and ports, the appetite to play these games without going spelunking into the often pricey second hand market is going to remain, meaning any such takedown is only a temporary measure, and one that they could and should capitalise on.