"Why do people say Jordan is Palestine?"
Because that's what Jordanians and Palestinians have been claiming for decades:
"We are the Government of Palestine, the army of Palestine and the refugees of Palestine."
-Jordanian Prime Minister Hazza' al-Majali
"Palestine is Jordan and Jordan is Palestine; there is only one land, with one history and one and the same fate."
-Prince Hassan of Jordan
"The Palestinians and Jordanians do not belong to different nationalities. They hold the same Jordanian passports, and have the same Jordanian culture."
-Jordanian Prime Minister Abdul Hamid Sharif
That's confirmed by the so-called "Palestinians" own leadership:
"Jordanians and Palestinians are considered by the PLO as one people."
-Farouk Kaddoumi, Head of the Palestine Liberation Organization's Political Department
"The Palestinian people does not exist. For tactical reasons, Jordan, which is a sovereign state with defined borders, cannot raise claims to Haifa and Jaffa, while as a Palestinian, I can undoubtedly demand Haifa, Jaffa, Beer-Sheva and Jerusalem.
However, the moment we reclaim our right to all of Palestine, we will not wait even a minute to unite Palestine and Jordan."
-Zahir Muhsein, Palestine Liberation Organization Executive Committee
So do yourself a huge favour: Realize you don't know what you think you know.
And sit down and shut up till you actually get educated on the subject.