Intermittent fasting doesn't suddenly change the laws of thermodynamics. Of course if you still eat 2,500 calories a day you will likely gain weight unless you already have a lot of muscle (but if you do, you likely know what you're doing enough that you're not reading this article actually hoping to learn anything).

The point is that IF makes it easier to reduce calories, in part psychologically but also in part because it's just a lot harder to eat 3,000 calories in 4 hours than it is to eat 3,000 calories in 12 hours.