"alternator workshop" warning

[McDub]

car's working. don't you just love how easily NRMA seem to be able to get cars started!

turns out there wasn't enough oil pressure for the lifters IIRC.
he turned the key for like a minute, and could tell from the sound what was going on, so he keeps cranking it, then the display reads out "STOP", then it reads out a low oil pressure warning or something like that, and then eventually, as it starts to sound healthier and healthier, the engine starts up!
was very surprised the battery had that much power in it.
who would have thought, you just keep turning the key if it doesn't start...

He checked the oil and commented on it being very dirty, so it's degraged a fair bit i think, there's still enough in there, halfway mark.
It last had the oil changed ~8000k's ago. Castrol Edge 5W-30
So should i either change it more often or change to a different oil?

another thing, before i did the last oil change, it had been 20,000ks since the oil had been changed, and when i went to check, the dip stick came out completely dry!!!! (i know i know)
Why didn't my low oil level warning light come on then?