Bald spot can be caused by a bang on the head?

[epipapilla]

Scott Walker, a USA Republican Presidential candidate says the bald patch on his head is the result of a scar he received from bumping his head while fixing a kitchen sink some years ago:

http://www.bbc.co.uk/news/magazine-34023654

[epipapilla]

Well, actually, I know that hair can stop growing in places on the scalp where a scar has occurred from a accident, as my younger brother has this situation, but he is 100% not bald and 100% does not have thinning hair.