I asked the locals why this guy (who was half in the light and half in the shadow) was praying in the narthex and not going all the way into the church with everyone else during the service. They told me that this was because he was a penitent who "confessed a grave sin" which earned him this non-admittance into the general congregation.
Nobody knows for how long he will not be praying with everyone else (or what is the sin he confessed of course).
I could not stop looking at the guy trying to guess what was that "grave sin".
The locals also told me that in the past praying in the narthex was mostly for catechumens.