22days post ureteroscopic kidney stone removal&stent placement still passing stones not on CT? Scans show nonobstructing stones how can this be?

Possible. It is good to pass the stones- obstructing or non- obstructing is only a matter of size of the stone and diameter of the ureter ( which is the tube from kidney to the bladder) small size stones may not be seen on ct. Check with your doctor- if kidney stones is a recurrent issue, may benefit if you see a nephrologist who can do some special tests and advise preventive measures.
good if stones come. After the manipulation with the ureteroscope and placement of the stent, whatever sediments that are sometimes not visible on ct scan or what ever the stone that got broken from the big nonobstructing one, they come out& it is good. Your urologist should be informed about the stones still coming out as based on that the need for rpt imaging, scopy, keeping the stent for more period will be decided.
Stones vs. debris. Material passed once you have a stent in place can be accumulation of calcified material around the stent or stones. There's no way of telling if that is stone matetial from your kidney or calcification from the stent without interval imaging. Hopefully your stones pass along side the stent & your gravel laden pee subsides after the stent is removed. :-).