It doesn't, any more than "from the river to the sea".
The only way you can think "river to sea" slogan implies genociding the Israeli occupiers is if you can't possibly imagine any other way to transfer ownership than brutal imperialistic colonizer-like expansion. You know, like what Israelis are currently doing to Palestinians.
Framing it as "you're calling for genocide" is just another way zionists try to conflate criticism of Israel with antisemitism.
It seems to me like people like this are telling on themselves that they're stuck in Colonial/imperial mindsets and lack imagination.
If I had to guess, it's because up until now you've held the assumption that the people in power know what they're doing for the most part, and nobody was a dying felon in his last years on earth terrified of going to prison for raping children.
Now you are under no such illusions, and the people in charge ARE dying felons that rape children and have no morals, and the government doesn't even want to try and check or balance itself.