Unless one entered the taxi with US dollars. Yet in theory the exchange rate should match inflation. To me the joke would only make sense under hyper-deflation.
This joke is essentially the opposite of debt deflation (theory of recessions), as described by Irving Fisher;[1] the theory states that the debtor loses money during deflation, causing repayment problems. In the bus/taxi joke, the rider is a debtor, and the taxi driver is a creditor, with the length of the ride being the term of the loan. The inflation is essentially devaluing the loan.
But 100 pesos at time T (bus) is worth more than 100 pesos at time T + interval (taxi)
"During the Brazilian inflation of the earl 1990s, for instance, supermarket workers reportedly spent half of their time replacing old price stickers with new ones." -- Essentials of Economics