Checking fixie for damage
I would certainly give a lot of attention to the chainring and lockring. One question that I think you need to answer is whether the lockring was loose before the incident or did the chain jamming the cog cause the lockring to come adrift. Then you need to consider whether the lockring loosened naturally, i.e. did it turn along the thread, or was it forced sideways? 

Do you tend to use a rear brake? From the question I get the impression you don't. (This isn't a criticism - I don't have a rear brake on my fixed, either.) 

If you use back pressure a lot when slowing and the lockring had been a little loose (when was the last time you checked it?) then it might be that that was what helped contribute to the jump - this is probably the best case for you, certainly the case with the least likelihood of damage beyond the tyre's flat spot. 

If you're sure that the lockring and cog had been tight before the incident, then I would really give the threads a careful review because you might have stripped them and caused some lateral damage. 

Given the jam, I would certainly be looking at the spokes: go round the wheel, both sides, just trying to gently flex each spoke, they should each hold firm; listen for creaks too. It also never hurts to pop the bike in a stand and just run the wheel round a few revolutions and watch its line - even if the spokes are all firm, you might see a little wobble. 

And if you're really thorough, go over the chain and check for bent links (and while you're at it, give it a good wipe and a lube, you can't do that enough).