Firstly I don't think they mean "TTL", its a 3.3 module, no doubt CMOS (everything is CMOS now!). Looking up the chip
part number from the photo might give chapter&verse.
But back to the plot - it is possible to use diode gating, but it gets more complex(*) (2 diodes and one resistor per input),
and using logic ICs is simpler.
(*) diode to ~10k resistor to +5V on each input, then parallel diodes from the diode/resistor junctions to form a diode
or-gate with 3.3V output - level shift one diode drop up before the diode or gate.