I'm fat but barely gained weight?

I got a Snapchat memory today from 2 years ago and I had a really defined set of abs and I looked great. Fast forward to today and I'm 4 sizes larger and have a very soft belly developing, I jumped on the scales and to my surprise I had only gained 4 ibs I am very short by the way. Why is this though?
I'm fat but barely gained weight?
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