The charity shouldn't be allowed to make this claim in its press release (here) or blanket advertising campaign (ongoing). It's a bad faith claim which doesn't really benefit anyone.
Even if it is the case that weight is correlated with cancer, it's not evident that weight causes cancer. The scientist dances around this statement because he can't say it.
Even if it is the case that weight is correlated with cancer, it's not evident that weight causes cancer. The scientist dances around this statement because he can't say it.