An industry is booming if you're buying their products, and people use the same books to play D&D whether they're doing it in person or using a virtual tabletop. I admit this is more true for roleplaying games than board games, because you don't really need to buy a board game to play it on Tabletop Simulator, but Roll20 definitely sells a lot of WotC products, with their own value add (virtual tabletop integration) on top of it bumping the price a bit. Which arbitrary point you choose to start considering them to be computer games isn't important when it's the same industry either way.