There are several ways to go about it, like (in order of effectiveness): train your model from scratch, combine a couple of existing models, finetune an existing model with extra data you want it to specialise on, or just slap a system prompt on it. You generally do the last step at any rate, so it's existence here doesn't proof the absence of any other steps. (on the other hand, given how readily it disregards these instructions, it does seem likely).