Colorant is sold is various physical forms - but the form that I am personally most aware of is in solid rods, bars or ingots. The hallmark of colorant is that it is a consistent color throughout AND it is generally uniformly formed.
Cullet as you are probably are aware - is whatever excess they had in the factory - dumped on the floor to cool. It is rarely uniform in color (Akro brick cullet is a known exception) and is usually in broken chunks. Cullet usually has multiple glass types randomly distributed through it - being the product of dumped pots.
The other indicator that your piece (which seems from what I can tell from the photo to be of exceptionally uniform color and shape - as if manufactured that way) is that the colorant seem over-rich with metal flake. This seems to me to be an intentional over-saturation of the metal salts that give the glass its color.
If you would like me to examine a tiny piece of it for other observations - I would be pleased to do it.
Regards,
Alan