hemstitching vs sewing stitch

hemstitching and sewing stitch both are nouns.

Word	Noun	Adjective	Verb	Adverb
hemstitching	Yes	No	No	No
sewing stitch	Yes	No	No	No

As nouns, sewing stitch is a hypernym of hemstitching; that is, sewing stitch is a word with a broader meaning than hemstitching:

hemstitching: a stitch in which parallel threads are drawn and exposed threads are caught together in groups
sewing stitch: a stitch made with thread and a threaded sewing needle through fabric or leather

Other hypernyms of hemstitching include embroidery stitch.

hemstitching (noun)	sewing stitch (noun)
a stitch in which parallel threads are drawn and exposed threads are caught together in groups	a stitch made with thread and a threaded sewing needle through fabric or leather