I imagine this was designed at a higher level, then exploded to smaller parts. For example, usually a 7-segment display controller is used to translate an input

I imagine this was designed at a higher level, then exploded to smaller parts. For example, usually a 7-segment display controller is used to translate an input value to one usable by the display, but it looks like he soldered one up manually. Similar to inlining functions in software, but all done manually in hardware.