and it takes 1 calorie to heat 1g of water by 1°C, so with your daily recommended food intake of 2000kcal you could heat 2000l of water by 1°C or raise 20l of water from 0°C to 100°C.
Also a normal person can rides the bike between 0W and 100W comfortably, while trained people peak at around 1000W for short sprints.
Given the craftsmanship on display here, I bet 10 money that they used the most simple way: hammering a nail slightly larger than the screw through the spoon (which is not that hard, especially if it’s silver).