Sediment in chicken stock
A stock made from roasted chicken is never going to be clear like a consomme.

You will note in the the video you reference, the stock is also moderately cloudy with some particles floating around in it.

This is normal, and nothing to worry about.

If you do desire a more clear stock next time:


Bring the stock only to the most gentle of simmers to reduce the amount of sediment stirred up from the boiling action.   It may be easiest to do so by putting the stockpot in the oven rather than doing it stove top.
Strain the stock with a very fine strainer or chinois, lined with several layers of cheese cloth.


In truth, I would suggest this is not worth it for most applications, unless you feel the appearance of the final dish being created is marred.  Since aspics are no longer terribly popular, where a clear gel really is needed for appearance, normally getting a very clear stock is not needed.