Once i started it, water started to flow from the hose connected to the water heater, into the main floor drain, and i instantly smelled strong paint thinner
Interesting. It would have been interesting if you had caught the first sediment in a bucket to see what settled out. It sure does sound like the smell came from the sediment in the water heater. You have already done a lot of searching. My search would be maybe
sediment "water heater" smell
If you saw much black, it would probably be from sulfur in the water. Yet I would have figured you would have noted sulfur smell previously. It is possible that the water source changed or somebody added a sulfur filter before you moved in, but a lot of sediment sat on the bottom of the water heater. Still, I have a hard time picturing some kind of strong smell at the bottom of your WH without a smell in the hot water. It's a mystery.
In flushing a water heater, you want to drain it, and then suddenly turn the water back on (but don't fill). Repeat several times. That makes turbulence from the dip tube spraying water at the bottom to stir up more sediment. The valve on the side of the WH can be unscrewed and temporarily replaced with a 3/4 NPT nipple if you want a bigger hole. If you have a pressure washer, you might even be able to get the nozzle in there. I did not do that.
You did not say if you have been there as long as the water heater. You did not say if you were on a well-- even a community well.
It looks like a good idea that you cleaned your water heater. I am a fan of inspecting and changing the anode. That is often much more difficult than it should be, requiring a big-enough impact wrench with a 1-1/8 impact socket. I bought a powered anode (not cheap) and put it into the old water heater after I moved in. But I ended up putting a backwashing sulfur filter which probably made the powered anode overkill after I gotten the powered anode delivered. Still it was good to pull out the old eaten-away anode. I figure that the powered anode could be moved to my next water heater anyway.