It’s been a while since I operated the 737 but I remember it coping pretty well with icing conditions - most jets with bleed air wing and engine anti/de-ice do. Only once after extended holding did we add a bit to Vref and it was obvious from the buildup on the wipers, etc. that there was significant icing.
Anyway, if the flight under discussion was seriously iced up, enough to badly affect the aerodynamics, I would have expected the problems to occur as they slowed down on the approach or loaded the wings as they pitched up at the start of the GA. Neither of these happened but there does appear to have been a sudden LoC after accelerating to a speed with a much greater stall margin.
There may have been ice involved with this accident but it seems unlikely to be a direct result of contamination affecting the flying characteristics.