It's interesting. I don't think the RF have / had anything to gain by leaking the meeting. They had plenty of positive press last week: the French visit, Wimbledon and their approach so far has been to ignore H&M and never to explain or complain, despite extreme provocation (Oprah, Spare, Netflix etc)
H&M otoh are probably interested in:
a) Gauging public opinion on a return. I'd suggest they don't need a meeting for that, the majority of the British public dislike them based on the data here -
https://yougov.co.uk/politics/articles/52165-royal-favourability-trackers-may-2025
b) Reconciling with the RF if it means they're financially supported, get security paid, are integrated as part of the BRF again
If there was something seriously physically or mentally wrong with Harry (other than the stuff we already know about, paranoia etc) it would be managed privately, it wouldn't be Meredith attending a meeting which was photographed.
IMO the meeting was set up by and leaked by H&M. Charles must have known it was taking place but I doubt he wanted it publicised. And if they did leak it, yet again they have proven themselves untrustworthy.