The slogan of the Houthi movement (officially called "Ansar Allah"), a Shia Islamist political and military organization in Yemen, reads "God Is the Greatest, Death to America, Death to Israel, A Curse Upon the Jews, Victory to Islam"
But would you put that on your flag? Because that's what the Houthi's did. Their flag is basically a Shia extremist written reenactment of that scene from Half Baked: "Fuck you! Fuck you! Fuck you! You're cool."
Some sources state that it was first chanted at the Imam al-Hadi school in Marran in January 2002, while others claim that Hussein Badreddin al-Houthi used it after seeing footage of a young Palestinian dying in his father's arms during the Second Intifada in 2000
Well it seems like they're confusing Judaism with Zionism. They should be explained the difference because their anger is clearly misdirected.
As for the rest, it's pretty normal if you look up what America has done to Yemen.
I don't know enough about the houthis to come to a conclusion about them as a whole, but the specific action of blocking shipping in response to the genocide of Palestinians is based.