Low IBU brews

Brewing Processes
1

I’ve been wondering lately how some beers, mostly porters and stouts, sometimes have IBU ratings of 10 or even less and are still not too sweet?

Is that achieved by increasing the amount of black roasted malt?

Thanks in advance for your replies.

2

Yeah, roasted malts can add some perceived bitterness and good attenuation can leave the beer not finishing so sweet.