The motive behind his assassination is still unclear, but it is indeed a possibility and it shows one of the reasons why the forces associated with the government in Aden are having difficulty dealing with the Houthis.
Their forces are not really united and they are very susceptible to infighting due to the tribal nature of Yemeni society, units with different ideologies/goals (Salafi units x southern nationalists, it is difficult to hold together a large force where one is unionist and the other is separatist).
Some PLC factions fight each other over oil fields, take the revenue and send little to nothing to the Central Bank of Aden.
Another reason is the overall incompetence of the Rashad al-Alimis government and its lack of authority, some parts of the PLC in Yemen are actually controlled by the local tribal warlords, rather than the main government.
The Houthis are not fully united either, they still have to deal with the tribalism of Yemen and force some Sunni tribes to cooperate, but they are in a much better position than their rivals.