"Oh," Peter said eyes widening just a bit and he shook his head, "No, no it's not like that - at least it wasn't when I did it. I worried about that too actually." He admitted, but Bulbasaur had been all too eager to follow him around so it seemed mean to just abandon it after it had sort of imprinted on him.
When she told him about the dog she'd used to know he couldn't help but grin and nod, "Yeah it was a lot like that, I don't think anyone is forcing them to come back with us, at least I haven't heard about anyone doing that - they seem to like bonding with people."
Peter held out his hands helplessly in a shrug, "I don't know what to tell you - it's some sort of tech they've developed here that lets them fit inside, as far as I know they aren't uncomfortable in there, it just makes it easier to travel around with them, and from what I saw there are some people who collect lots of them so if you have the balls you can carry more of them pretty easily." The hows of it all were a bit outside of Peter's realm of expertise, at least for the time being - if he got another pokeball he might be able to poke at it and maybe figure something out, but right now he just worked with what he'd been told by the locals.