The guy could NOT have gone too far in the wrong direction because we now know that he was with his buddy for 25 minutes on an 80 foot dive. Even though he had a big tank, he had used up a good portion of his time and air in the general vicinity of the correct dive site (which is more or less straight north from the drop point).
In any regard, since the capt picked up the lost divers buddy only 5 minutes after she left him, he would have a pretty good fix on where the diver was last seen and since she was reported to have indicated that her buddy was "missing", it would be reasonable to assume that the capt. might mark the site on his GPS or make some other mental note as to this particular location, since it is relevant to where he should expect the diver to surface (even if he did not foresee the eventual lost diver situation).
The area is dove very frequently in the summer with literally a hundred divers per week drifting through this general area located just a mile or so from the inlet, so it is pretty unlikely that he found a stash of "gold bars".
I agree that it is very surprising that with the perfect conditions that day and the capt. presumably getting an intermediate fix on the diver (half way or more through his dive) that this guy was not found (not withstanding the abscence of an SMB).
The conditions were also somewhat unusual that day in that there was a noticable thermocline and the bottom (cold) water was moving north, but at a much slower rate than the surface current. This does tend to widen the possible search location if the searchers do not know WHEN the diver transitions from the slow current on the bottom, to the faster current on the surface.
Definitely an unusual situation for a diver to get "that" lost under such good conditions.
