Pretty hard to tell what it is from pictures. It could even be many coats of BLOicon but determination of that would have to be at your end. BLOicon won't be a hard coat which is what it looks like on the upper surface next to the barrel and on the metal parts.

My preferred removal method is spray on citristrip which you can find at Walmart and a lot of other stores in the paint removal department. It isn't caustic, is water soluble and does a good job of cleaning most finishes and even some dirt which yours doesn't have. It's also fast. Take the action out of the stock, place it in a shower or bathtub and spray a good coat on. Let sit for 20 minutes and wash off. A scrub brush might be helpful if the finish is thick. Second application if needed and rinse again. Generally dries in a few hours and you can start coating with BLO. One can will generally do three stocks.

You could try rubbing it with alcohol first. If it is a type of shellac, that should take it right off. Shellac along with tung oil and BLO all tend to have a yellowish cast.

A third option and maybe the easiest would be a rub down with light steel wool just to get the gloss off. It doesn't look bad as is, is protected, just a bit too shiny.