Of course, they mean 50 years of "occupation" by Jews.
Because no one was overly concerned about the previous 19 years of "Palestinian territory" being annexed or administered by Jordan or Egypt.
Or the 30 years of British administration before that.
Or the 400 years of Ottoman rule before that.
No, the only interest in what the world now calls "Palestinian lands" only started when Jews have some level of control over them. Not when generations of others - Muslims and Christians, Arabs and non-Arabs - controlled the land.
Somehow, only the years when the life expectancy of Palestinians skyrocketed, when the infant mortality rate plummeted, when practically all of the universities and major hospitals were built in the territories - only those years are considered tragic.
The entire exercise of "50 years of occupation" is underlined by blatant hypocrisy. If there was no Six Day war, the West Bank Palestinian Arabs under Jordanian rule would be just as interesting as the East Bank Palestinians are today - meaning, not at all. Gazans would remain in an effective Egyptian prison, with no ability to move to Egypt itself - but no one would be talking about it.
The self-rule that most Palestinians in the territories enjoy today would never have happened.
And no one would be writing op-eds about it.