I suspect your opponent was in provisional state, where he in fact has two MMR. That happens when you play the first 25 games after a long break, and increases the MMR variations upon each victory/defeat by quite a lot. It’s also possible you were playing very late at night, where the players pool is reduced by a lot. 
That’s possible. It seems the amount of players start decreasing around silver 3 and below. However there are quantities of them in gold, so it seems strange for a silver 3 to be matched with a gold 1 (2.8K) if there isn’t some additional twist involved.
A quick league progression and spontaneous macro capabilities are better reflection of skill than just APM. Don’t forget that some races just induce higher APM, and that a lot of players just spam to increase it.
Actually there is more difference between a 2.2K and a 3.2K MMR player, than between a 5.0K and a 6.0K.
It happens that I’m currently surveying battlenet around silver. The APMs I’ve seen there so far were between 18 and 70, with some rare zergs sometimes reaching a bit more than 115.
In platinum (2840MMR to 3.2K) APM is frequently between 100 and 150, with some protoss around 65 and some zerg around 250 (not counting smurfs).
High APM doesn’t implies skill, but too low APM straight implies a lack in core mechanics, specially in Z and bio players.
A platinum could beat a silver by a large margin while offracing for the very first time (I remember having done so on a welcome match for one player of my clan, I wanted to do some kind of 2Gates poke to show him the meta but messed up the gaz income (first time playing protoss), so I ended up doing the poke with three zealots… and the worse is that he didn’t even react, so I circled his stalker with slowlots XD… and from there took the nexus. I don’t think that kind of misplay (bad opener, holed wall, absence of kiting, absence of workers pull) would be possible if matched against as low as a gold 3 player. 
