It comes from the full sentence
The portion before the comma I translated as "I noticed that/a guy", as the character just woke up in a dark room and is hearing voices around him in the dim light. The portion after the comma I am confused about. Does it mean anything literally? I think it's basically a string of particles with a "questioning" {{JP:ねえ}}, an "inquisitive/forceful" {{JP:のか}}, and a determined {{JP:よ}}. With that I guess that it gives the reader the feeling that the character is uncertain whether to be happy or afraid that he/she has noticed this other person.