No, I think the DEM is the minor reason, but rather the CCI Landcover product which is additonally integrated. Again, please read the commend of Jan here: SNAP Tutorial - #13 by Jan
I wouldn’t trust any of them, to be honest, as they are automatically derived from every image based on robust routines. But they do not replace an adjusted classification. And the cloud masks are rather an indication for image quality, but also not ultimately correct.