The term pilot in nautical or aeronautical parlance means the person who takes charge, e.g. ships take on pilots to navigate tricky waters, the pilot taking over navigation duties from the captain. Hence the term "pilot" in railway usage generally means the lead engine, where a loco is attached ahead of the train engine.
Back in the days of steam, when shunting of coaches and wagons on and off trains was common place, "station pilots" were often provided. I suppose the term kind of makes sense, as it is the loco in charge of shunting moves at a particular station. Must admit that I had never heard the term yard pilot used before, though, I have always heard them referred to as yard shunters (or various local derogatives, such as "the donkey").
Shunters or shunting locos is usual UK parlance, as opposed to switchers in US - although I think switchers can cover quite large distances in the US. The Ffestiniog Railway used to have a "bottom shunter" for shunting between the stations and yards at the bottom end of the line, and likewise a "top shunter" for shunting between the quarries and stations at the top end of the line.