You bought a used car which the previous owner had replaced the stock steel/hub-capped 195/60/15 or 16" dual-spoke aluminum alloy wheels with customized (gun-metal/black) GTS single-spoke GTS wheels.
I think the problem is either you are looking at FACTORY STOCK specifications and trying to compare them to what's on your new used-vehicle -- or you were sold something which was advertised as stock and you got a free upgrade.
There is nothing wrong with having GTS wheels on your GT. Enjoy your upgrade Also, if I recall correctly, mainly the GTS models were pre-equipted from the dealership with genuine Action Package body kit installed. The chances are, that if you have a GT with an Action Package body kit installed, the previous owner was the one who had the work done, and quite possibly did additional work to it as well, such as the wheels.
EDIT: check this link https://www.celicahobby.com/forums/...ns-and-Options-GT-vs-GTS.html#Post449235
And this one, too: https://www.celicahobby.com/forums/...e-Size-Speedometer-Error-Calculator.html
How do you like your new Celica so far?