The RSPCA have responded to me
‘Thank you for your email.
Our colleagues have reviewed your concerns and their response can be seen below:-
I was able to locate the page with dietary advice for guinea pigs you're referring to, and although I believe that broccoli and kale were listed as examples of suitable leafy greens rather than recommended as the top two green vegetables guinea pigs can be fed daily which could of course cause implications for their health I can see that this is not entirely clear in the paragraph so will request for the advice to be changed.
Best wishes
RSPCA Advice Team ‘
That’s great news I think