Turn signal blinking fast

Flipping through my 1991 GM Factory service manual, it defines short & ground just as you have. Then it says "short to ground" throughout the manual!

GMC Gremlin

I will go with a direct short to ground. And as you pointed out earlier, the blinker control can be acting faster than the fuse or circuit breaker.

I had a wire that had worn a hole and was shorting to ground but not blowing a fuse. First symptom was a dead battery. Got a jump start and no problem for a while. Then one day after turnng off the engine I heard a clicking noise under the dash. I was able to slide under and saw a wire that was shorting out, heating up, expanding the wire and breaking the short, cooling off and shorting again. Of course eventually the battery would be so low that it would just sit there and totally kill the battery.