I think its just his name - & the 'helm' element doesn't necessarily mean helmet - it had a range of meanings in Anglo-Saxon:
Quote:
|
helm [] 1. m (-es/-as) protection, defence, covering, crown; summit, top (of trees); helmet; 2 protector, lord;
|
This is a decent Anglo-Saxon dictionary
http://home.comcast.net/~modean52/oeme_dictionaries.htm
Elfhelm/Aelfhelm is a fairly common Anglo-Saxon name & I suspect Tolkien simply liked the sound of it.