I agree that the images are more than would be expected if HQ were used as a stabilizer. Sulfite is used as an antioxidant as well, but the most common chemical used is TAI (Tetra Aza Indene) and its derivatives which are not developing agents by any means.
And, in some papers, I have see a full toned image develop with just alkali in spite of the mfgr stating that the papers are not developer incorporated.
Ballasted HQs are used in the interlayer of color materials at the rate of about 10mg/ft sq. This is far from enough of the HQ to develop anything considering that it is ballasted and has a high MW. Its purpose there is to scavenge wandering oxidized color developer and prevent cross layer color contamination.
Kodak used TAI, PMT (Phenyl Mercapto Tetrazole), Methyl Mercuric Iodide and Cadmium Nitrate among other chemicals to both tone and stabilize B&W materials. In addition to those, Agfa used Lead Nitrate, Cupric Chloride and several other organics. After about 1960, Kodak began using all organic salts for toners and stabilizers.
But, many EK papers develop a full B&W image with only alkali.
PS. Most stabilizers are present at about 100 mg per or less mole of silver or about 100 GRAMS. This is certainly not enough to develop any sort of an image.