This is taken from the article I gave:
"The technical term for this behavior is Resource Guarding, and it�s an absolutely normal dog behavior. However, it�s not something we humans appreciate. Fortunately, resource guarding is also a behavior that we can change."
All dogs will resource guard at some times in their life, therefore it is perfectly normal.
The pup is not trying to be 'top dog' (how on earth would a six month old pup try to be leader of a pack!). There is no such thing as 'top dog' or Alpha, the leader of a pack of wolves (and dogs are not wolves) constantly changes according to what the pack is doing at the time.
Besides this way of training has been proven to be based on flawed studies of captive wolf packs. If you really want to know how wolves behave then read this by Mech who studied wild wolf packs for many years.
http://www.4pawsu.com/267alphastatus_english.p df