The problem is the schematics. The schematic for a particular type of gate is what it is, with no regard for what is connected to the output. The video truth tables depend on changing output connections, whereas correct ones do not. Electrically, his OR and NOR schematics are identical, two diode cathodes connected together. This is such a common logic implementation that it has its own name: Diode-OR. What you do with it might make it behave as an inverted-input NAND (the DeMorgan equivalent), but that has nothing to do with the positive logic function of the gate.
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Diode-or circuit - Wikipedia
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