he is using it in the sense of 'to start', as in it is the first discrepancy he notices. it struck me as a bit plain, the masai are usually very colorful. the size of the one you are considering would be useful. see below for comparative sizes. i've seen childrens ones and ones 'for those who travel' of a foot to 18" or so (30-50 cm.)
here's some masai participants from the london marathon:
another masai in full warrior dress
google 'masai sheild' and go to images for a LOT of examples, new and old.
part of one page: