Probably poor seamanship or maintenance, but being UAE flagged, Iran or their Houthi rebels in Yemen would be the prime suspect if there were foul play.
Car carriers in particular tend to be pretty unstable if not ballasted properly for the cargo loading. This size ship would likely be in coastal trade and not cross ocean. A safe bet is that the captain by error or intentionally to save a bit on fuel use was sailing light and the weather won out.
BTW, what the ballast water is for is to keep the ship's center of gravity at a designed point and to correct trim for an excessive list via cargo loading variance. It's the captain's responsibility to calculate and implement ballast requirements before leaving port.
gcaptan has good details.