The explanation I got for logic board was from the classic all-in-one Macs. They had a high voltage “analog board” for the CRT, and the low voltage digital “logic board” for the CPU.
IIRC the rationale was a logic board has a soldered CPU, but IBM calls it “System Planar” so yeah
Apple calls motherboards as logic boards making non-apple devices look illogical piles of electronic components. :)