Presumably because they're smoothing it with the lawnmower-sized ground-compacting machine, rather than a full-sized roller. That's what they used when they put a tarmac surface on Birmingham's towpaths (because the banks couldn't take the weight of a roller), with similarly lumpy results that can be quite tedious on a non-offroad cycle.
I'll still take smoothish lumps over actual potholes, though, so as long as it's not used as an excuse to skimp on full resurfacing when needed.