The question that has to be addressed is whether Ansar Allah, the movement generally called the Houthis, represents Zaidism. The short answer is that it is Zaidi in derivation and is not the Zaidi religious establishment.
It grew from Believing Youth, founded in 1992 at Sa'dah as a Zaidi revivalist education movement, running summer camps that drew fifteen to twenty thousand young people by the middle of the decade, in direct response to Salafi expansion into the region. Hussein al-Houthi militarised and politicised it after 2003 around opposition to the United States and to Israel. He was killed by government forces in 2004, and his brother Abdul-Malik has led the movement since. It took Sanaa in September 2014, seized the presidential palace in January 2015, and assumed power through a revolutionary committee in February.
Bernard Haykel has characterised its reading of Zaidism as highly politicised, revolutionary and intentionally simplistic, departing sharply from the classical scholarly tradition. Many established Zaidi scholars dispute its religious legitimacy, and critics allege a drift toward Iranian Twelver practice, which the movement denies. In the areas it controls it has in places displaced the traditional Zaidi religious establishment rather than represented it.
Population figures should be given with care. Zaidis are usually estimated at around a third of Yemen's population, on sources that are dated and not census-derived; Yemen has had no reliable religious census, and war since 2015 makes any current figure guesswork. Global totals in the tens of millions circulate and are poorly supported. There are also Zaidi communities in the Najran region of Saudi Arabia.