Though they have the Holy Spirit (unlike the natural man of 1Cor. 2:14) they were not behaving like spiritual people, but like carnal – that is, fleshly -people, like immature Christians (babes in Christ).
There is a difference between being fleshy and being fleshly. Fleshy is simply made of flesh; it can speak of the weakness that is common to every fallen human. Fleshly, when used of a person, means characterized by the flesh. It speaks of the one who can and should do differently but does not. Paul says that the Corinthians were fleshly.