He was not talking about Pace's pure snow, he was talking about the stuff we had in UK which, according to all the met reports and forecasts I read was mostly RASN - mixed rain and snow which can (even according to Pace's theories) adhere to the airframe because there is visible moisture.
I think you're missing the point. For ice to adhere to the airframe, you need an airframe that is at a temperature below freezing, otherwise the ice just melts off very shortly after it adheres by heat transfer from the airframe. Generally, the airframe will only be below freezing if the air temperature is below freezing. And if the air temperature is below freezing, you'll get snow, not sleet (RASN, in the UK sense of "sleet").
So why might there be liquid precip but the airframe still be below freezing? One possibility is an inversion, where the precip has passed through an above-freezing layer before falling into colder air again. But that will be freezing rain or ice pellets, not sleet. Another possibility is that the airframe is still cold, having come quickly from a colder environment with e.g. wings full of cold fuel that take a while to warm up to ambient. But again that's not an issue about snow, as the icing that you get in such conditions is likely to be as bad if not worse if the precip type is rain rather than snow.