In 1973, Goodyear and Firestone were supplying all race tires for Nascar, and they were slicks.
Nascar did NOT race in the rain.
At least not on speedways. (Firestone retired from Nascar in 1974, leaving Goodyear to be the sole supplier)
There were a couple of road race courses on the schedule at that time, like at Riverside California.
I guess it's possible there were treaded tires in case they had to run Caution laps in the rain,
...back then, Caution laps counted as race laps, so rather than stop a race...
but, I highly doubt it.
The cars did not have wipers so driving in the rain would have been an issue.
This seems more likely that the model was copied from one of the clone cars that exist
and those often drove on treaded tires so they could run in parades and on streets.
Just a theory.