@niculinux:
You've got to stop and think about XPiratez as part of XCom. It's almost an entirely different game, but not quite. Doing things to prisoners always makes them disappear. It is no different for XPiratez since it is build on XCom.
Either the prisoner dies or gets released as part of the bargain, but after one interrogation, they're gone. Otherwise you could milk them for all their random topic (especially bad for high rank enemies). Interrogating a certain unit will enable robbing/enslaving/taming of that unit type. That specific unit disappeared, but interrogating it told the runts how to "process" subsequent ones, once you catch them. This enables the robbery and slavery manufacturing projects.
In your specific case, you interrogated an altar boy and he told you about stuff in exchange for his freedom (because the gals felt like being nice for the poor little dude after the handling). While interacting with him, you've learned how to convinced altar boys to serve you as squires, so the next time you catch one, you can enslave him. That doesn't make a slave out of the first one, since he was released, but you can enslave the next one. Or just rob him, since now you know what kind of valuables the kid has in his possession.
