If the turbine threw a blade causing it to fly apart, then the resulting debris punctured the generator causing the hydrogen used to cool it to explode. I saw that happen to a gas fired steam plant near Dallas back in 1974. The turbine tripped off at about 1AM but a LP turbine intercept valve failed open and the residual reheat steam caused the turbine to overspeed and it disintegrated as the bearings ran out of lube oil and locked up. The hydrogen in the generator exploded causing a fireball that was seen in downtown Dallas. Parts of the turbine and on shrunk on ring on the generator shaft were found up to 10 miles away.
The control room was right on the turbine deck and was shredded, but no one was badly injured. I got the full story from a guy who was a shift supervisor at Comanche Peak who was a SS there at Mountain Creek that night.
If they truly did have a highly localized geomagnetic storm there, yes it might have contributed to the disaster by tripping the plant and a stuck opne isolation valve might have caused an turbine overspeed that caused the turbine to disintegrate.