I think anyone in this kind of situation would have taken any chance they had to get themselves a lighter sentence even if it meant pleading guilty. It seems this was the case and I know many of us if put into the same situation would have taken the same decision.
The government (both federal and state) tends to charge people with very serious crimes with harsh potential punishments and then offer a plea deal in which they get a very minor sentence.
It almost always makes sense to plead guilty unless you can prove your innocence as it is too much of a gamble to go to trial.