My guess (and its just a guess based on past observation of how the Commission manages Mahoning Creek)) would be that the musky fishery there is probably the result of fingerling (or even fry, for all I know) plants and that fish from either the river or the lake (above the dam) don't augment the musky pop. in the creek much, if at all. If there is some augmentation, its probably in the section just upstream from the junction with the Allegheny.
Over the past 20 years, give or take, they've tried a variety of different management plans for the creek below the dam. Back in the 90's, I think, they loaded it up with walleye fingerlings. I don't think they took hold though. Also, maybe in the later 90's or so, they tried to establish a stocked trout fishery immediately below the dam. I don't think that worked out either. So, I guess they're trying it with muskies now and it must be working out.
It would seem to me that the top section of this stretch below the dam, say upstream from where 28/66 bridges it, would be less than ideal musky water. But what do I know, I'm not a fisheries biologist. Anyway, I used to fish it a lot for smallmouth and there weren't very many holes of any consequence in this upper section. Lots of flats and shallow runs. Or at least that's how i recall it.