Note that they're also VERY close when they do that. They simply know the spread on all weapons' hip fire and do it only when it's roughly within the width of a character model. Also, it's same as with PK, you have to be EXTREMELY accurate to get good dps out of a spread that just about covers the character model, because any millimeter off the target will lose damage. While with 100% accurate ADS, you have leeway to be less accurate with your crosshair placement and still hit the target with every single bullet.
So if you're not 100% accurate with your crosshair, you must hipfire even closer than that max range. I myself only hipfire when my gun is literally in their face, otherwise ADS is better for me.
You're generally NOT SUPPOSED to be using hipfire at any non-super-close range. The fact that ppl with perfect aim can do it at mid (well mid of cqc, 5-20 meters) range does not mean that you should be doing it as well (unless you also have the aim for it).
The only weapons that you generally never ADS with are PK and Eva, since they both have exactly the same spread both in hipfire and ADS. Wingman and p2020 are very accurate in hipfire, but it's just better to have the crosshair as their ADS movement speed is almost 100%. Moz and mastiff has a little higher spread in hipfire, but that usually results in A LOT lower damage, so generally better to always ADS. Triple take is the only sniper that is accurate in hipfire (but only viable very close, since the spread of the 3 bullets is also affected).
SMG's are quite accurate up to 10 meters, so hipfire is used often. AR's are not very accurate in hipfire, but their ADS movement speed is turtle-like so often losing damage to dodge opponent's damage is still acceptable in CQC. It's still probably better to fire ADS-bursts and move between them rather than go full-on hipfire at 10+ meters with AR's.
P.S. I think spitfire's hipfire spread is quite wide (just test it on a wall to get a feel for it before committing to it in a fight), better use devotion if you want to hipfire with an LMG (much higher dps too, so you can even miss more and still outperform the spitfire).