This is an exaggeration just as the wrong as the pensioners who think they carry all the weight of the Thai economy.
A tourist spends a high daily average for 2 or 3 weeks, but a lot of this money does not arrive at the Thai economy, it goes to foreign companies, Hilton, Emirates etc. Of course, these big lump payments are easily taxed by brown envelopes, so decision makers in Thailand like them.
Pensioners spend all year round, not only two of three years. They spend lump sums that go directly into the Thai economy, like condos, cars, washing machines.
Their daily average i do not dare to guess. I know pensioners whose daily average is incredible low. Personally, I spend much, much more per day since I live here than when I was a tourist.
in aggregate, tourists are, of course, much more important because they are many more.