I call BS!@
I weighed equivalent bikes, on the same scales, in the same shed, using the same method.
Both using rad braces, AXP bashy, P3 Pipe guard, and everything else stock. The 13 a kick only model, the 18 with the magic button. There was 5-6kgs difference, both with about a quarter of a tank of fuel (111kg vs 116/7).
I always thought the 13 felt heavy to lift. I never really had any issue with it in motion. I haven't lifted the 18 yet.