Very simplified it means taking a big budget, spreading it across many channels to get rapid feedback, and scaling according to this feedback.
for example, if im a facebook OR adwords specialist, i might build my strategy around just one, and will not always think about mixing them up (any many other strategies and media types)
A SEO in most cases will not suddenly try to mix hes game with Paid traffic, UNLESS it will benefit hes SEO game - which i consider a SEO growth hack.
As i see growth hacking - its either you implement a new style of Sales Funnel, UI, UX which will convert WAY better than the verticals avarage - but it will always go with 360 marketing which will attack the consumer from all angles and every strategy will be also a kicker to the other ones. (retargeting Native Ads traffic on facebook or google, create Awarness on mobile - Retarget on Desktop, PPC / SEO a direct amazon listing for manipulating ranking etc)