This is not unique to the Falcon, and not unique to FM23 - it’s been an issue in multiple Forza games for years, whereby any Ford is classified as being American even if it was a Aus- or Euro-market only car (such as the Sierra, Escort, Cortina etc). Turn10/PG really need to either transfer the country of origin tag to the individual car rather than the brand, or split out region-unique models in to separate brands, for instance Ford (Australia) and Ford (Europe), basically the same as what is done with Infiniti/Acura/Lexus being badged as American (the first two are reasonable but arguably Lexus should be moved back to Japan as it is truly global and not primarily NA-market)
There are a couple of cars where the reverse is true, ie an American-market only car being listed as coming from another country (the main ones that comes to mind are the Nissan 240SX and NISMO Sentra) but not as many.