I think he's talking about double dippers. The fact that this is a late port will indirectly lead to some more sales for the other versions, and those same people will end up getting a second copy on switch. This tactic worked with games like GTA V on PC (and MHW), although this is on a lesser scale, of course.
So he's talking about the combined sales of the game, not just the switch version.
Another reason I think is to not overshadow that other dragon ball game on switch (whats it called again?), and give it some time to breathe.
I know what he is talking about, but it fails to happen like that more often than it does. In many cases, the amount of people that just pass on the game altogether far overshadow the double dippers.
Example, I wanted Wolfenstein II for Switch, so passed on the PS4 version. Now almost a year later, Wolfenstein II is out for Switch but my time is taken up by other games instead. If they released day and date, they would have my Switch purchase. Now they have nothing from me.
That tactic can only ever work on games that have MASSIVE sales like GTA5. And most people I know that got MHW on PC waited to buy it at all for that version. I doubt double dippers did much for MHW in this case.