I think that the point is that there is nothing that you could really "separate as a part", everything being fused into a single piece impossible to disassemble without destroying it.

This is to put in perspective with a Zoom Lens where moving parts are designed to be assembled and disassembled: https://www.lensrentals.com/blog/2021/01/the-secret-of-the-b...

Also, a heated metal bar dilates and thus moves, not sure it is considered having "parts".