First, some background
You've probably already read this in the rules, but "tons" measure volume, not weight. As described on page 42 of the Traveller core rules, the "tons" used in traveller are actually "displacement tons," i.e.: they represent the volume of fluid that would be displaced by the thing whose tonnage is being measured.
As mentioned on page 142 of the core rules, each represents about fourteen cubic metres of volume - a cube about 2.4 metres to a side, the size of a small room or large closet.
"About 14 cubic metres" might seem like an arbitrary value, but earlier editions of Traveller specified that it was because Traveller's d-tons were "displacement tons of liquid hydrogen fuel," one metric tonne of liquid hydrogen takes up 14.28 cubic metres.
The rules don't answer your question
Unfortunately, the rules don't specify whether the 10 Kg baggage allowance of a basic passage passenger is part of their living space, in addition to it.
As you've noticed, most other forms of passage assume that the cargo space is separate to their the passenger's living space, so it'd be sensible to assume that basic passage follows the same rule - but basic passage is weird. It was apparently designed to let players ignore carrying capacity limits that were a key feature of earlier editions, and 10 Kg is a tiny amount of cargo to keep track of compared to the multi-ton cargo holds of most starships.
Basic passage is unique to Mongoose Traveller, second edition
It's not found in any other flavour of Traveller. Most other editions of the game put a limit on how many people a ship's life support systems can handle, and tie that limit to the number of staterooms on the ship. This makes the idea of keeping passengers outside of staterooms a non-starter, rendering any question of how much baggage space they need moot.
The fact that basic passage doesn't appear in any other edition of the game means that there's no precedent from earlier editions that we can draw on.
If I were GM...
Still, were this to come up in a game that I was running myself, I'd almost certainly rule that the 10 Kg of baggage was either part of the basic passenger's allotted space (and that they spend most of their time clutching their belongings for fear they'll be stolen by another desperate refugee).
Alternatively, I might rule that the 10 Kgs of baggage does take up space in the hold, but that it's such a small amount of space that it isn't worth tracking. I mean, 10 Kg is only 1% of a ton, so you'd need 100 basic passengers on a ship for their combined baggage to take up even 1 ton of space.
Either way, it's just not worth tracking such a negligible amount of cargo. (I'm sure most basic passengers would disagree with that policy, but you get what they paid for, and they paid very little.)