There is a difference in meaning between 'these' and 'those', both in English and in Czech. The Czech sentence here uses 'ti', which means 'those' or 'the'. This DL course is 100% consistent about this.
Those horses are not yours... because they dont belong to you.
Those are not your horses... because they dont belong to you.
I would say the meaning is the same but the words are not.
Is it wrong because the Czech 'tvoji' is plural and not singular?