From Sword Art Online Volume 3 - Fairy Dance, Chapter 2 (emphasis mine):
"[...]. Yggdrasil...she seems to be there. That place, you know
"Ah, this I know. Eh, eh, it's generally to the northeast, but quite a
ways from here. If I were to convert it into real distance, it would be
about fifty kilometers away."
"Wow, that really is a long distance. That’s what, five times the
diameter of Aincrad. Actually, why was I brought to this forest anyway?"
Yui lowered her head for a moment at my question.
"I think that your positional data was either damaged or confused with a nearby player, resulting in you ending up here. That’s just a guess, though."
In the screenshot, the pyramid like structure is the signature building of the Spriggan hometown. The blocky void above it is the glitch that "teleports" Kirito to the forest.
Yui raised two possibilities for the glitch:
Kirito's positional data was damaged
Since Kirito and Asuna was teleported to the sky outside Aincrad in SAO moments before the game shut down, and Kirito's character data from SAO was loaded in ALO, chances are that the positional data was also loaded, which sent him on a free fall nosediving trip into the forest 50 kilometers away from Yggdrasil.
While this matches the fact that ALO's map is much bigger than SAO (as seen in the above quote), it was quite a miracle that Kirito dropped right at the forest where Leafa was. As the map in ALO is much bigger, he might as well had ended up elsewhere in ALO.
Kirito's positional data was confused with a nearby player
Since Kirito and Suguha were accessing the game from the same IP address (which is quite common for IPv4 in real world), Kirito's positional data got glitched up and he was dropped in the forest where Suguha (Leafa) was, instead of the hometown of the Spriggan. The fact that he fell from the sky matches the fact that Leafa was having a mid-air fight.
I admit this is a bit stretching, but this is the closest I could relate a real life concept with the theory above to explain the proximity of Kirito and Leafa's position in the game and the timing when the glitch happened.
(Either way, I take it as an excuse for the story instead of general knowledge).