So I'm just curious because when I was younger I was skinny fat and had the typical skinny fat soccer body, something along the lines of a young Beckham.

Well now I've thickened out over the years and put some years into training my core is becoming thicker? I guess would be the best word for it.

Essentially I went from:
https://www.apsense.com/blog_photo/20121215/1355624215276506.jpg

to this:
https://themanimalsguide.files.***/2012/08/screen-shot-2012-08-14-at-8-26-57-pm.png

or this:
http://vivendilab.com/wp-content/uploads/2014/12/dan.jpg

Stomach-wise of course (not saying I'm that lean, I mean the abs on the 2nd photo appear to stick out more)


Is it genetics or would cutting a bit more flatten out my stomach, or is it just muscle tissue/fat?

it could be a lack of training your transverse abdominis (basically your natural "belt" around your waist) and your stomach is protruding because of it, or you could have lordosis of the spine causing your hips to tilt back too far and your stomach to protude.
check out https://www.t-nation.com/training/best-exercise-for-a-smaller-waist or google vacuum exercises to train the TVA band.

that being said it could be from other things like gluten/lactose intolerance causing your gut to be inflamed etc.

It's almost 100% genetics when it comes to core. But then again, you can see a small change over the years.

More than likely none of this

dat roid gut

hgh

What then?