Give @KevinWhite a biscuit / cookie for being first to point out that 'Traditional analogue meters were reversed'.
Your meter manual hasn't got a schematic but if you do an image search for 'analog multimeter schematic' you should be able to trace out the battery positive going to the - socket in most of them.
Figure 1. A 'simple' analog multimeter with the typical devious circuitry. Note that there are two batteries for the resistance ranges and both head towards the '-' (black) socket. [Click for full resolution.] Source: Vesselyn.com.
It's weird, but when you think of it the meter deflects towards full-scale when current comes in on the red lead. Therefore the current must come from the black lead.
I tested a simple rectifier diode with the same ohmmeter. I got meter deflection with positive probe on cathode, but no deflection with positive probe on anode. Does that help?
Your results from your diode test confirm that the black lead is more positive than the red on resistance measurement ranges.