Wow that was quite a beard before the trim! I suspect the "thin spot" was an artifact of the trimming itself. I know when I trim back a big beard, sometimes there seems to be spots that get a little more of the blade than others for whatever reason.

Patience shall be rewarded!

New beard growers: Check out the Rules of Beard Acquisition.
To upload and post pictures, here is a tutorial.
Do you believe in these Common Beard Myths?