What Furukawa means is that due to smartphones being everywhere, there is no need to expand the gaming population anymore - because most people these days are already gaming! That, of course, does not mean Nintendo will only target an older core demographic.
Quite the contrary: When two of your big current games are 2D Mario and a more casual version of Pokémon and your heaviest hitters for 2019 are Animal Crossing, Pokémon and a more affordable Switch Mini (+ Yoga Watch in Japan) you are clearly trying to expand your user base. But these casual gamers already are gamers these days, so there is no need to explain the concept of gaming. Instead, you can target your mass market software at a hot market instead of a cold one like they had to do with Wii / DS.