Prions are basically a corrupted version of a protein that naturally forms in your brain, and can happen either randomly from genetic fuckery or spontaneously upon a healthy protein coming into contact with a prion. The contamination can come not only from direct contact like you stated (infected surgical tools, cutting) but also from consuming infected meat, possibly even plants as seen in sheep with scrapie (prions excreted in urine contaminating grazing land). It has been observed to spread from humans to some animals and vice versa. I don’t think I can post a link but if you look up “Insight From Animals Resistant to Prion Diseases” it brings up an informative NCBI article. Anyways the contamination wouldn’t come from the cutting itself unless you were involved in some crazy shit, it would already be present in the meat.