Yes, the cuphea is sometimes called heather. More often it's false heather, though.

But usually, it's called wax weed.

And Cuphea and Calluna aren't even in the same family: one is in the Lythraceae (like loosestrife and henna) while the other is in the Ericaceae (like uva ursi, rhododendron, and bilberry, to mention a few).

The only thing they have in common is their looks: they're both compact shrubs with pink flowers.

And there's a lot of small shrubs which grow on bare, rocky places. Flower color is completely incidental.

Yet here's a website which mentions both in the same sentence ... http://www.innvista.com/health/herbs/heather/

They're not interchangeable.

Heather (Calluna vulgaris) is a nice herb to make you sleep (if you pick only the flowers), or to strengthen your kidneys (if you pick flowers + leaf).

False heather (Cuphea spp.) is a simple astringent.

I'd have put up two different entries.