It follows directly from his example. Inflation means that you need to invest your money into something (i.e. either use it directly to buy goods and hire people to produce a product or service and sell it, or else lend it with interest to someone else who will do so on your behalf).

In essence, an inflation economy is one where the only money that is not in immediate circulation is the one that is currently reserved for anticipated imminent transactions (i.e. the bills in your wallet, or in the cash register before the end of the day) - which is a tiny amount. Everything else is parked in some bank account, investment fund, stock etc, where it generates interest for the holder by being loaned out to someone else who currently needs it to produce.

So with some non-zero inflation, you maximize the utility of your monetary tokens as medium of exchange.