@exxp he means he's not aware that he's been spacing out the whole time unconsciously, for someone who think he need to be aware of everything and fully in control he's shocked that he's doing something without himself realizing it.
Maybe its just one of those cases where you start zoning out and when you come to your senses you realise that someone was there directly in front of your field of view so it looked like you were staring at them the whole time. Happened too many times in class for me, so awkward trying to explain that I wasn't actually staring at them.
Gawsshhhh thank you sooooooo much....lately, none of my followed manga and manhwas have ever...eeeevvveerrr updated in the past few hours and day, I think, this was truly life saving