I will try to address this owing to my experience in managing multiple products in internet and digital domains.
"Growth Hacking" is a term coined first by Sean Ellis (founder of GrowthHackers.com). However rather than talking here about jargons, what I have realized based on experience is -
Growth hacking is all about experimenting with multiple ideas in a way which can be measured against a clearly defined goal (that goal generally is an improvement of any of the important metric).
So one simple example of growth hacking is say your business sends out newsletters every fortnight. So two goals probably around your newsletter would be to always better the open rates and then the click through rates (say you have some links in that newsletter). Now in a growth hacking culture, you will need to always innovate with headlines, content layout, placement, theme to determine what combination is working for your target audience. Startups focus on this bit more rather than following a set pattern of newsletter.
So in real scenario, it need not be that one person has to be expert in marketing, tech and product. I bet not many will say that they are expert in all these :)
To get more details, you can check my post here - https://www.linkedin.com/pulse/demystifying-growth-hacking-nishith-gupta?trk=prof-post