1. This is exactly the case of all those geo-minn-ed (geominn-ed) incels. A real 5/10 person, with the right geo-maxx (geomaxx) is not going to be an incel at all. But if he's in a place where the women are "Chad only", "Prettyboy only" and "Mega rich only/Mega popular only", well then, this is it. Very, very high standards.
2. If the person is geomaxxed enough (i. e. living in a place where even a 2/10 may have a chance if he's with the good personality, stable income and other basic things) then maybe it's a mental problem (mentalcel's inceldom) or something really serious (like disabledcel's inceldom, poorcel's inceldom). Otherwise a 5/10 (looks) person can't be an incel there; only a volcel.
3. There are also other possible cases like these: he's a 5.5/10 but he's too short (i. e. a shortcel). Or he's just photogenetic (looking attractive in photographs but not in the reality) (i. e. not more than 3/10 which isn't enough in most of the places around the world). There are also fakecels (for example he's having a girlfriend or broke up recently) who just like to pretend (or really think) that they're incels.