Stainless steel that gets coated is no longer stainless steel. Stainless steel requires exposure to sufficient oxygen in order to maintain the protective oxide layer.
These are rudder bolts from the same gudgeon on my sailboat. The black stuff is anoxic corrosion.
Pssh… This guy is chump change, maybe a senior engineer at best. You can tell by his footwear. The really highly paid engineers have Crocs with socks, if any footwear at all. 😆