I don't believe this for a second. Nintendo knows where its goldmines are. IMHO it is far more likely that they steered clear of mobile because they didn't want to cannibalize their Game Boy sales. It's a classic case of a big corporation being slow to react to change or even trying to stop it because they hold a dominant position in the old system.
Nintendo would much prefer if "mobile gaming" still meant Game Boys but the world has already made their decision and they can't stop it. They can't ignore the sales figures on what would have otherwise been an obscure goofy spinoff fitness app on the Game Boy. They've ignored the mobile market for too long and now there is pent up demand. Without Pokemon Go I doubt you would have seen the sudden scramble to develop and release a Mario game for iPhone.