This is even kind of hinted at in the article. The symptoms people are presenting with are different from classic monkeypox outbreaks, and as far as anyone can tell the actual disease hasn't changed and this is all due to the route of transmission.
Previous Monkeypox outbreaks have not been linked primarily to sexual transmission. It may be that the initial cluster of the current outbreak is caused by people meeting up for sex (although really, who knows?), but given what we already know about the disease, it would be unwise to jump to the conclusion that sex itself is necessary for efficient transmission.
If there's really a consensus among experts that sexual transmission (rather than just transmission via contact during sex) is playing a key role here, then by all means reference this. I've been unable to find anything of the sort.
>most of the spread so far being amongst the more sexually promiscuous parts of the gay male community...
Here you're moving away from informed speculation (which is already unwise at this early stage, in my opinion) and simply repeating sensationalist nonsense from less reputable sections of the news media. There is absolutely no reliable data on how 'promiscuous' the people who have been infected so far are.
"The clinical presentation is often atypical, with few lesions localized to the genital, perineal/perianal or peri-oral area that do not spread further, and an asynchronous rash that appears prior to the development of a prodromal phase (i.e. lymphadenopathy, fever, malaise)." [1]
[1] https://www.who.int/news/item/25-06-2022-meeting-of-the-inte...
For example, the 'atypicality' of the presentation could simply be a consequence of MSM who are used to getting sexual health checkups being more comfortable with showing their genital sores to a doctor or nurse than other population groups.
I'm not sure if the presence of genital lesions is necessarily even a good indicator that transmission was via sex. See e.g. https://academic.oup.com/ofid/article/4/4/ofx168/4588539