Here's why:

* Open clusters are relatively young groups of stars, formed from the same giant molecular cloud. They are loosely bound by gravity and are often found in the disk of the Milky Way galaxy.

* Globular clusters, on the other hand, are much older and denser, containing hundreds of thousands or even millions of stars. They are tightly bound by gravity and are found in the halo of the galaxy.

So, while a few thousand stars could be considered a small globular cluster, "open cluster" is the more accurate term for a loose grouping of this size.