How much is en masse? There are enough people relocating to my town buying homes with cash, from the sale of their much more expensive homes, that it makes buying a home for the current residents very difficult.

I'd say they were more wealthy for their property value and converted that value into liquid wealth by moving locations.

Why would selling houses en masse be necessary condition to call the owners wealthy? The mere ownership makes them wealthy, not their selling activities.

This is just ad-hoc changing the definition of wealth to suit your particular need at this particular time.