I'm sure they can sell more than that tbh. I find the 50% upgrade for April-Jun more impressive.
From the way the article reads, it seems Nintendo has only for now increased there production projections for the April-June time period and not yet for the rest of the quarters this year. So Nintendo expects to produce 2 million more Switches during April and June than once projected at the beginning of the year. Which likely means they need 50% more parts than originally expected during this time period.