I'm looking around my local bike shop and saw that the hybrids have a slim tire while a mountain has a more fatter tire. And when i researched it says the opposite. Please help me.
Could you be confusing diameter with width? Hybrids often have 700c wheels which are a larger diameter than 26" wheels more common on Mountain Bikes. The tire widths fitted to 700c tires are narrower than the mountain bike tires. As user973810 says the width comparison normally goes as you observed from road bike to mountain bike.
The dimensions aren't made any less confusing by the switch between metric and imperial, i.e 26" vs 700mm. Ditto for the widths.