Why not read the article? Here you go:

Until recently, most cases in Congo resulted from consumption of contaminated meat or close contact with infected animals and people. But last year, scientists discovered a new subtype of mpox, Clade Ib, which appears to spread from person to person primarily through heterosexual transmission.

From a recent BBC article:

Mpox is transmitted through close contact, such as sex, skin-to-skin contact and talking or breathing close to another person.

It’s a pox virus. The vehicles may change, but it’s related to other pox viruses like smallpox. Primarily through skin contact, which can include sex. The fact that it’s spreading through children is a bad sign, though, as schools are a big vector.

“Sex is probably the primary driver, and then the secondary driver is close contact and households,” said Dr. Jay Varma, the chief medical officer at SIGA Technologies, which manufactures tecovirimat, a drug used to treat mpox infection.