I get that, but the little bit of music between the verses in the example I gave are not a few bars of the melody - that snippet of music is completely different to the main tune of the carol. When we sing that carol at home that bit is simply not there. In the Carnival Band version, that fragment is a deliberate part of their arrangement. When I think of it, and especially when I think of emulating their version with my band (which may never happen!), I regard that little segment as a riff, as it's repeated insistently through the song (occasionally varied, admittedly). Anyway, riff or not, it's a lovely version and it's one of my Christmas favourites!