The exploit for the non-warlocks.
For the quest: The Humanoid Cannonball - Quest - World of Warcraft
Anyways, I noticed this immediately after watching a few warlock's and their summoning circle.
If you manage to land close to, or near the circle or on land. You can simply bunny hop to the circle and gain the 5/5 or 4/5 for "landing" inside of the circle.
Since you currently retain land movement speed while you jump out of the water (While swimming) this makes this 'sploit a bit easier.
Steps:
1.) Pick up quest
2.) Get launched from the Cannon
3.) Drop the wings and land close to the circle.
4.) HOP to the circle without stopping to obtain credit as if you landed in the circle.
This method requires a bit of work, but it's an easy alternative instead of precisely landing into the circle itself. I found this by myself, and if someone else has found this before me I sometimes lack the mind to search prior to posting. If a video is needed I can post a video later.