5NGQ, chain E has DLS (di-acetyl-lysine) bonded to DCY206. So the acetyl fills the N-C gap, not an oxygen.
FG finds this one because FG is looking only for a Cys/Dcy/CSO sulfur gamma within 3.1 Å of any nitrogen that is not (a mainchain nitrogen or a sidechain nitrogen in (Asn/Gln or the D forms of those, Dsg/Dgn)). So the N can be in a ligand or a non-standard residue such as DLS.