A peak detection charger watches the charge current and battery voltage. It does not detect heat (ok, well some will but not most) so if it was charging too hard it could easily overheat and explode w/o tripping the peak detection circutry.
You did not say what charge rate you had set but as foxy said charging at 1C is about the best balance of time and rate.

Two other quick thoughts...They say not to charge a battery unattended for a reason and second, aren't you glad it wasn't a lipo?? If one of those had done that it would probably have started a pretty good fire.