Again, that first study from the 2003 doesn't talk about lesions inside the anus or on the penis. Perianal (your words) is not the same as perineum (what it says in the paper).

Please, continue the copy paste from the second report.

it is noteworthy that a substantial number of our cases who were young adults in their reproductive age presenting with genital ulcers, as well as concomitant syphilis and HIV infection. Although the role of sexual transmission of human monkeypox is not established, sexual transmission is plausible in some of these patients through close skin to skin contact during sexual intercourse or by transmission via genital secretions. The role of genital secretions in transmission of human monkeypox, however deserves further studies. Our findings also suggest that HIV-infection might negatively influence the morbidity of human monkeypox as patients with HIV had more severe skin lesions associated with genital ulcers as compared with HIV-negative individuals.

So 5 years ago they started talking about sexual transmission as something to look into.