This article from ESPN/BASS isn't bad: The Ultimate Guide To Supercold Smallies however, there are a number of things that jump out at me. Super cold water smallmouth bite cutoff being mentioned at 39F, maybe throwing jerkbaits alone (in general), but.... It also seems BASS/ESPN article is behind the times a little. There are more than a few internet smallmouth sites that discuss 'super' cold water fishing in depth these days and on a continual daily basis. Many of the limits the BASS article puts on winter bass fishing are commonly exceeded by regular Joe, winter smallmouth angler.
I don't know exactly how cold the water was pushing ice flows off to sea and catching fish underneath, but I am certain smallies bite very well in 33-38F water. In my experience, it's the weather, direct light, and current height(CFS)that matter most in 'super' cold water.
Example 1, say you have 36F ultra clear water (4'+ vis),low flow, bright sun, and plenty of ledge rock for smallies to hide under. They aren't going to be easy to catch because of the low temps. They'll be hard to catch because the cover allows them to hide under things that prevent any sort of proper presentation. These fish are lethargic and not at all confident in their abilities to hide from percieved predators above! In this situation, I'd fish a winter pool with little cover and enough depth that you cannot fully see bottom.
The same weather with stained water, the same fish are now quite catchable as they are up and moving somewhat in the current of the slow water. Smallmouth are paranoid, light shy, probably never more vulnerable than when their metabolism is so low. The seek the security of darkness/shelter. If they cannot find it, will hunker down. These clear water/bright light situations lead to more 'the fish aren't biting' days than anything. Maybe they are biting, but under undercut banks and such-inaccessable.
Fishing creeks and seeing to what length smallmouth will go to hide from light in low clear water on a small manageable scale (you can eliminate behaviours based on less behavioural options in a smaller stream, (the behaviours at least locally translate on a larger scale)- under sycamore trees- in the hollowed out banks beneath the roots, under those hanging carpets of small roots dangling the stream banks, wedged under rocks, in drain pipes, laying in leaves,etc... smallmouth bass have the complete ability to disapear if they are inclined.
In winter, this all happens still with the caveat the fish have to be able to survive cold high water events. There are more days when the big fish is plum in the middle of a eddie and catchable. That hog is probably limited in it's activity hours compared to warm months when you have a smaller chance of catching it feeding and liklier chance it'll be hid.
It part of what makes them so fascinating to target.
Example 2, medium flow or greater, good green stain, 36F water, snowstorm, and decent water visibility. The color cuts down on the light penetration, Mr Smallmouth feels safe. Uses the slight current of the eddie or slack pool to hover about the circuit looking for an easy meal. Bigger fish have more energy reserves, while small minnows do not. Must be easy pickings. The incoming storm warns the bass that they should feed or risk not having the energy to survive possible high water event to come (storm).
So why do smallmouth diehards fish the Winter bite? The opportunity to learn about stream bass is at its greatest in Winter. We can get a sense of just how much energy a cold blooded stream bass has, another glimpse into how it thinks.
Which leads onward to catching the elusive brown whale.