I didn't know this story until today, but it makes perfect sense.  This little nugget was in Killer's Q&A on MLive today:

(question): " ...  What is it about general manager Martin Mayhew's approach to the draft that is different than Millen's approach considering that there was very little turnover in the scouting department?"

Tom Kowalski:  "...I've often recounted the Brian Calhoun story, about how the Lions were debating about whether to take an offensive lineman at that spot in the third round. The argument was whether the Lions would be "reaching'' for him at that spot. They went back and forth without resolution and then, as the clock was about to expire, a coach yelled "Take Brian Calhoun.'' And that's what they did.

That situation won't happen with Mayhew running the show..."

So while some (coincidentally, more successful) teams would rely on their scouts' research, and iron out their draft board ahead of time, our previous regime would get everybody together to argue back and forth, and then draft the guy whose name was shouted at the right time.

I can't think of a more fickle, haphazard way to make critical decisions short of randomizing the whole thing.  unbelievable.