Normally 'proper' sti's have other performance bits, different interiors firmer suspension etc, if you open the bonnet and yours has a red manifold it's a full blown sti engine, they also have badges in the cabin & on instrument cluster.
But with yours being an import the Japanese love to customise them and there's a chance the original owner ticked loads of sti extras on the options list. so if it's not a factory sti then it's got some expensive goodies on [emoji16]