Most people these days understand the concept of 'hair extensions'.
SO many girls have them.
And so it would be possible to describe it as an 'integration' of extra hair to bulk up your own... like extensions.
If they want attachment details you can explain they're just like extensions in that they can be bonded, clipped or woven into your existing hair.
Keep it simple and keep it light and then people kind of accept it on those terms, like its not such a big deal.
If they ask to see it up close, you point out that if its well done, there should be nothing to see.
Its a question of being dismissive and deflecting.

Otherwise, if you make a bigger thing of it then you'll find in future those people you've told have a habit of talking to the top of your head as they're still intrigued.

The fact that people want to touch your hair is, in a way, a good sign because it shows they don't think of it as anything but your own.
But stopping them is a different matter.
I had transplants that everyone knew about (and the majority of them still think thats what they're seeing) and so I would say that my head had loads of scar tissue on the scalp and touching it made me uncomfortable.
I also made a bit of a joke about "NOT TOUCHING THE HAIR" because I'd spent ages grooming it.
Unfortunately, with more casual styles (and they're the sort people seem to want to touch & ruffle) this doesn't apply.

But if you've explained the hair extension thing, then it wouldn't be unreasonable to say thats why you didn't want it messed with.