The answer to this lies in the Carry Capacity details.
With a strength of 16 a medium creature can carry 230 lbs at maximum heavy load. A Choker, being small, can lift 3/4 this amount, or 172.5 lbs. Furthermore, a creature can lift off the ground up to double their maximum heavy load (in this case 345 lbs), or drag up to 5 times (862.5 lbs), although when doing so, they can only stagger around at 5ft movement speed as a full-round action.
The average human male weight is about 165 lbs. The single most significant addition to this would be armor, and (in my experience) breastplate armor is the most common type, thus adding 40 lbs. We can say maybe another 40 for various other gear (weapons, backpack, tools and rations, etc.), bringing our total to 245 lbs. This is outside a heavy load for a choker, but still within possible lifting range. And considering that they don't tend to move about much, it is unlikely to be care about the movement penalty.
And this is giving the adventurer a lot of benefit as well. The Choker is only CR2, and unlikely to be encountered at levels when the adventurer could afford breastplate, let alone such heavy armors as splint mail or full plate. No, the adventurer is more likely to be equipped with lower quality and, more importantly, lower weight armor like studded leather or chain shirt, making the Chokers assault a bit easier. And woe betide the poor wizard who only has Mage Armor and a spell book to his name, as he'll be hoisted right up with no problem to the Choker whatsoever.
Also, Choker's don't generally lift their prey into the air, instead reaching down from their hiding spot on the ceiling to choke their prey.
That all being said, neither the carry capacity rules, nor Improved Grab say that it gives any bonus to lifting capacity, so it doesn't.