Do you have any source for that? I don't think that is the only reason some people say it is occupied. There are many less preposterous reasons
Since June 1989, Israel has formally restricted the movement of Palestinians, imposing a magnetic-card system whereby only those with such a card were allowed to leave the Strip: Israeli authorities did not issue magnetic cards to released prisoners, former administrative detainees, or people who had been detained and released without charges being filed against them.[37] January 1991 marked the beginning of the permanent closure policy, whereby each resident of Gaza who desired to travel within Israel or the West Bank was required to have a personal exit permit.[37] In March 1993, Israel imposed an overall closure on Gaza with newly built checkpoints; and, from October 2000, Israel imposed a comprehensive closure on the Gaza Strip.[37]
When the Al-Aqsa Intifada broke out in September 2000 Israel put trade restrictions on the Gaza Strip and closed the Gaza International Airport. The economic effects worsened after the creation of a ‘buffer zone’ in September 2001, that would seal all entry and exit points in the Palestinian Territories for "security reasons." After 9 October 2001, movement of people and goods across the ‘Green Line’ dividing the West Bank from Israel, and between the Gaza Strip and Israel, was halted, and a complete internal closure was effected on 14 November 2001.[38] The worsening economic and humanitarian situation raised great concern abroad. According to the UN Conference on Trade and Development (UNCTAD), in January 2003, the Israeli blockade and closures had pushed the Palestinian economy into a stage of de-development and drained as much as US $2.4 billion out of the economy of the West Bank and the Gaza Strip.[39]
When the settlers left in 2005, within 2 years Hamas was elected and Israel further tightened restrictions resulting in a total military enforced blockade. Fishermen are often shot and harassed on the coast, and gunboats have shelled the beach causing fataliites on numerous occasions.
In September 2007, the Israeli cabinet voted to tighten the restrictions on the Gaza strip. The cabinet decision stated, "the movement of goods into the Gaza Strip will be restricted; the supply of gas and electricity will be reduced; and restrictions will be imposed on the movement of people from the Strip and to it."
It may be technically unoccupied as IDF does not conduct checkpoints or have any other presence as they do in the West Bank, not considering the Gaza buffer zones. But blockade is too tame a word for the situation in gaza with regards to Israel