Possible stiff wheel rotation causes for your scenario:
1. Brake adjusted so it's being applied. A quick check would be to see if you have any free play at the pedal. Then try backing the adjuster all the way off.
2. Chain too tight. It would have to be pretty damn tight, but it could happen. try backing off the adjustment.
3. Rubbing on the swingarm (or something else) from misalignment. Have a close look all the way around.
4. Incorrect spacers and/or shot bearings.
Anyone think of anything else?
Just start at the top and go through a process of elimination. Do one and check for results, then go on to the next. If you get down to #4, you're getting into the unsafe to ride territory.
The pic you put up is the axle head. Think of it as the head of a long bolt... that's all the axle is, a long bolt. Your axle nut you tightened is on the other end. In between is all spacers. the swingarm axle plates act as spacers... there's external spacers you can see, then there's internal spacers you can't. Even the inner race of the bearings act as spacers... so that you can tighten the axle and lock all those spacers firmly in place, allowing only the outer races of the bearings to turn. What I'm gettin' at is that if all that is correct, over-tightening the axle nut is not really a thing....all you're doing is locking all the spacers more firmly in place. And that won't hurt a thing. If loosening the axle nut causes it to turn freely, you've got a spacer/bearing problem.
Did you notice if it spun freely before you first loosened the axle nut?
Was the axle nut good and tight at first or did it come loose easily?
You didn't remove the rear wheel, correct?