One thing that the automatic summary missed is this important paragraph:

However, Israeli Prime Minister Benjamin Netanyahu’s Likud party also echoed “river to the sea” phrasing in its founding charter as a way to say his government doesn’t recognize Gaza or the West Bank, according to Dr. Dagher, who was a Canadian government analyst overseeing Ottawa’s international aid to those occupied territories from 2007 to 2011. Still, she acknowledged that the phrase can be terrifying to Jewish people especially since Hamas has also placed the phrase in its charter as a call to erase Israel.

So both sides of the conflict have used the phrase as a way to dismiss the claims of the other, although it's origin is as a Palestinian slogan. According to this Wikipedia page, there have historically been multiple interpretations of exactly what is meant when using that phrase and those variations continue. In fact, as of this writing, neutrality of this article is disputed with the relevant talk page raising what could be conflicting concerns, most notably the issue of whether we take the meaning from the users' claims or from those holding opposing views.