Old Spock was on Delta Vega because he'd been essentially exiled (or, more appropriately, cast aside) by Nero on that planet1, specifically because (miraculously) it was close enough to Vulcan to see it being destroyed, but not close enough for it to be pulled in or otherwise affected by the black hole Nero created to destroy it.
It was certainly not deliberate: Old Spock had no say in the matter, and it's extraordinarily doubtful that Nero would have put him where Kirk would find him (to say nothing of the fact that, given how drastically they've already altered the timeline, neither of them could have had any relevant prescient knowledge of these events anyway).
Kirk arrived there by sheer accident, it simply being the most convenient place for Young Spock to drop him off when he exiled him.
So, yes, Young Spock just happened to drop Kirk off on the same planet Old Spock was on, and Kirk just happened to land close enough, and just happened to walk in the right direction, for the two to meet. So, yes, one big cosmic coincidence.
1 Not a moon! Vulcan has (had) no moon. Well, I guess it could have been a moon around a neighboring planet in the system, but could just as easily (and arguably more likely) have been said planet.