What is the difference between coming upon a foreign woman orally, anally, and vaginally? Do all of them necessitate stoning? And why do some consider oral coming to be a minor sin and not Zina (adultery/fornication) that necessitates a prescribed punishment?

It is absolutely forbidden to approach a non-mahram woman (ajnabiyyah) orally (meaning, to perform oral sex with her). This is considered a form of zina (illicit sexual activity) in the general sense, based on the Prophet's (peace be upon him) saying: "The two eyes commit zina by looking, and the two ears commit zina by listening, and the tongue commits zina by speaking, and the hand commits zina by striking, and the foot commits zina by stepping, and the heart yearns and desires, and the private parts confirm that or deny it."

However, it is not equivalent to the major indecency in terms of the type of prescribed punishment (had). The zina that incurs the hadd punishment is the insertion of the glans (hayshafah) into a forbidden private part (farj) without any doubt (shubha). Anything other than that, even if it is called zina, does not incur the hadd punishment. However, the one who commits it incurs sin and deserves tazir (discretionary punishment) and discipline. Oral sex is not considered the same as vaginal intercourse because it is not a place of cultivation (mawdhi‘ al-harth). Stoning (rajm) is not exclusively for approaching a non-mahram woman; rather, only the muhsan (married person) is stoned. As for the virgin (bakr), he or she is given one hundred lashes.