A lot of traditional European dishes (inc Swedish meatballs) mix minced pork with a darker meat, usually beef or veal. You get the savoury flavour and colour from the red meat and the mild flavoured fat from pork. It's a similar affect "grain fattened" beef produces in a single animal, but the animal doesn't need to be an obese cow.

If you have venison in a resteraunt, it's often rare steak dishes. It's cooked rare because it's so lean, and dries up when cooked for longer. Usually the meat is trimmed, because the fat/grisle isn't as good as beef (in ye old times, venison fat was used for tallow candles instead of lard) But, not every cut is steak.

If you make sausages or minced meat dishes (meatballs, etc.) from venison, cutting it with pork or pork fat makes it much more suitable for most recipes.

Lying to consumers is not ok, but combining venison and pork is legit. My guess is that it's traditional.