It would be only just if the Palestinians would get their own state after this.
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It's not their land to 'return to' - after all, people already live there and they have no moral right to displace them.
The idea of a nation called Israel is the invention of Zionists in the 19th and 20th century.
Palestine was never a country before 1948, immediately prior to 1948 there was a British Mandate[0] with the name Palestine, but this mandate included land that would eventually turn into countries like Jordan(which just so happens to be a country with a Palestinian majority population). After 1948 and before 1967 the West Bank was annexed by Jordan and Gaza was occupied and administered by Egypt.
The idea of a nation called Palestine is arguably a more recent invention than the nation of Israel.
Palestinian refugees are defined differently by the UN vs essentially all other refugees.
Palestinian refugees fall under the UNRWA while normal refugees(i.e. refugees from essentially all other countries) fall under the UNHCR. The UNRWA definition is hereditary while the UNHCR definition is not. This hereditary definition is largely why the Palestinian refugee populations can increase over time in other countries so easily vs normal refugees.
There were multiple reason they(or their ancestors) left, there was plenty of violence when Israel was created but it wasn't like it was just one side attacking either. Regardless it's quite strange that someone is still considered a refugee despite potentially having never even been to the country they are supposedly a refugee from, especially since that doesn't happen for refugees from other countries(at least with how the UN defines refugee).