Just my hunch but Iran is a founding member of OPEC.

The UAE has had a long standing land dispute with Iran.

The recent barrage of missiles might have just pushed the UAE leadership to have lost patience with their northern neighbor.

This might be an act of protest.

Probably Saudi Arabia is more important in OPEC, so that might be actually a middle finger to SA. Saudi Arabia and UAE had a recent dispute in Yemen that went pretty hot.

An alternative is the US trying to dismantle OPEC together with its new found supply in Venezuela to drive prices down