I believe it means they will call you when they want you to work, but wont guarantee 25 hours a week ect. It will make it much harder for already struggling casual workers to make ends meet.
Sad truth is stores like these will be obsolete soon. They already have to operate on thin margins, but with most game sales going digital, there will be less demand for brick and mortar game stores. The existence of online stores like Amazon make their outlook even worse.