The other comments basically reveal that every physical problem we try to understand requires approaching the solution using a mental model with built in assumptions and limitations. So, perhaps when we have a question or face a challenge when something doesn't make sense, it is good to look deep down through our pyramid of assumptions upon which we place our understanding. Unless we solve the problem, then all assumptions are suspect. For example, while others point out the probable main issue here (the metal's emissivity), there are other assumptions. There is the assumption that the metal, the other parts and air should all be at the same temperature. In fact, the problem is a bit complicated when you get into the slight differences. The objects each lose energy at a different rate by emitting (mostly) IR photons at different rates (paramaterized as "emissivity"). Additionally, the objects conduct heat at different rates. Since they all lose heat via IR to the cooler environment outside the chamber (which also irradiates the same parts, but with fewer IR photons), the parts will never purely reach the temperature of the air in the chamber. What equilibrium temperature each one reaches, down to the hundredths of a degree perhaps, depends on how quickly the parts can conductively and radiatively absorb heat compared to how quickly they lose heat via the same processes to the outer environment (via) IR, the inside air (via conduction and IR), and the parts they touch (via conduction) and the parts within line-of-sight (via IR). So, the problem is actually quite complex and only simplified if we don't care about small temperature differences. Plus, if we did care about such small differences, the measuring device would have to be highly accurate.