Yeah, I'd wager it was his laziness and proneness to shortcuts. One thing, though: Article states the radio show took place a few months after he won so probably 1984 or 1985. Federal Reserve website states that there were 7.5 billion one-dollar bills in circulation in 1999 (couldn't find numbers for years prior 1999). Increase of one-dollar bills in circulation seems to have fluctuated a lot over the course of years, might have been a significantly lower number in 1984/1985. I mean, it'd still be an impossibly long shot but I felt like pointing it out.

I was also thinking if the radio host was reading serial numbers from a specific newish year and the bank notes are more likely to be new then old maybe that would also increase the odds.

Yeah, but I'll pass on that. Give me a job at walmart over reading serial numbers all day.

Myth of sisphus

Depending on how the serial number was chosen, the odds could be dramatically higher, dramatically lower, or zero. If the serial number was derived from another, new bill, received from a local bank, then the odds are quite good.

If it is chosen by writing the serial number of a bill in your pocket, then circulating the bill by purchasing something. The odds go up if you happen to stop by the banks a few days after that happened, or they go to zero if the bill was not fit for circulation and it was removed by the Federal Reserve.

Also, there's a good chance that a random serial number is not actually valid.