I haven't tasted the GP, but I have some thoughts based upon what has been described here and what I know about some other products used in the food service industry (e.g., restaurants).
There are three things that strike me about GP : MSG as the second ingredient, and the natural flavor, and finally price.
MSG - it is very unusual to see MSG as the second ingredient on a spice blend label. Since the ingredients should be listed in order of weight percent, that suggests a fairly high level of MSG, certainly greater than 2%.
Natural flavor - I am going to go out on a limb and suggest that the "natural flavor" is probably in the grill flavor
category. There are a number of flavor companies that produce flavor concentrates for the food prep industry. Both Red Arrow and Kraft produce lines of natural grill flavors that are designed to emulate the flavor imparted by grilling. Some of them get quite complex, adding specific smoke flavors, a seared taste note, grill scraping, etc. as well as the base grill flavor. The starting pint for many grill flavors is simply pyrolysis (controlled burning) of vegetable oils. As an example of some of the flavors available, here is a link
to Red Arrow's Grill Flavor line; a link to Kraft's Natural Grill Flavor line
and their Specialty Grill Flavor products
These kinds of intense flavor additives are so effective they are typically used at the well less than the 1% level.
A spice blend made by McCormick produced for and sold to the food service industry (i.e., not the retail consumer) that uses "natural grill flavor" is their Char Broil and Grill Seasoning
. You can get the idea of what it's about here
The combination of something like a grill flavor with a high level of MSG would likely give a fairly complex taste profile that would be hard to pick apart unless you are a flavorist.
Price - At $3.99/lb the price of GP is on the very cheap end of spice blends. That suggests there isn't much of anything exotic or expensive in it.
As for charcoal - I doubt it. I don't believe charcoal is approved for use as a direct food additive (activated charcoal is used as a filter medium in food processing).
Finally, since there are no color additives declared the black has to come from the other ingredients.
Here's a question for the AL crew - does the store make this stuff, or are they repackaging a blend they buy ? The reason I ask is the label ingredients suggest a level of spice blending sophistication beyond what I would expect for a grocery store, and certainly not something likely done at the local store level. Maybe you can find out a bit more by asking them where it's made ?