By buying links, he refers to having his website link on a page with a page rank. This wud help the site to improve the page rank. So, inturn it brings traffic thru search engines as the website is displayed higher in the search listing...
Short term: Adwords gives you instant traffic which you can track ROI very easily. Long term: build links (although be wary of buying links as you may get penalized).
For me, backlinking and CPM show better results. However, I'd add that these things are not rather to be opposed. They use different strategies, so using both parallelly should contribute greatly to one's SEO achievements.
^^ Why do you need to buy yourselves a first rank in the SEO when your Adword place is already there?