It's TTS. They absolutely don't go dubbing around every line for this, that'd be insane. That's the whole point of this system, to provide some fun sounding audio for the lines without having to actually dub them. You can tell because they speak your island name and your own name exactly the same way as the rest of the text, accurately. And because it's pretty monotone and consistent.
Besides, can you imagine voice actors dubbing this stuff in this kind of voice line by line? They'd go insane.
Besides, can you imagine voice actors dubbing this stuff in this kind of voice line by line? They'd go insane.