Definitely follow up.
However, be careful not to fall into the trap about something being too specific for an X year old to make up. Kids have a habit of both repeating bit of pieces of things they've heard and joining it with other details. As you press them, they'll make more details up. My nephew, even at like 3 would make up these oddly specific stories about all manner of things. The more you talked to him, the more detailed the stories would get.
Part of what makes them especially odd are their ability to integrate, sometimes almost verbatim, fragments of things they've heard other people say.
However, be careful not to fall into the trap about something being too specific for an X year old to make up. Kids have a habit of both repeating bit of pieces of things they've heard and joining it with other details. As you press them, they'll make more details up. My nephew, even at like 3 would make up these oddly specific stories about all manner of things. The more you talked to him, the more detailed the stories would get.
Part of what makes them especially odd are their ability to integrate, sometimes almost verbatim, fragments of things they've heard other people say.