Concentration, is by my reading of the RAW, just mundane, real world concentrating.
Now I will say, one of the big questions I’ve always had is whether a character Concentrating on a spell is aware of the spell ends.
For instance, if Wizard casts Haste on Fighter, then Teleports back to base, 100 miles away. Fighter than gets DM’ed. Is the Wizard away he no longer needs to concentrate?
If so, it probably lends credence to there being a magical spell connection between caster and spell effect when Concentrating.
But my take has always been they wouldn’t know, because it’s described as mundane Concentration.