How?
The article is short on substance about how a 'reopening' could lead to more inflation.
Is it more people going out and spending money? Something else maybe?
Prices for a lot of goods -- gas, travel, hotel, etc -- have been in the dumps since COVID. It should be expected that prices on these goods will rise as the country opens up.
There will probably be a good deal of pressure on labor prices as well. I suspect that many people in the hospitality and service industries have changed careers rather than sit around indefinitely waiting for a 'reopening'.
The assumption is that as the pandemic ends that this velocity measurement will increase, that people will be out buying and selling things a lot more than they have been for the last year.
The size of the money supply was increased significantly over the last year, due to the trillions in federal stimulus injected into the economy. This was done presumably to prevent many businesses and households from becoming financially insolvent. This is also considered to be inflationary.