There is no difference in the principle of shareholding in a private company or a publicly listed one in the UK or in the USA. What difference there is, is that publicly listed companies have a hugely more onerous requirement on them as regards disclosure to the relevant financial authorities about their activities and trading records. 1 share in IBM gives you exactly the same rights as 1 share in Hasselblad as against those companies. The major difference is that you can always buy your 1 share in IBM because it is listed on the NYSE. You can only buy your 1 share in Hasselblad (a private company not listed on any stock exchange) if you can find someone who owns that share and is prepared to sell it to you. But the principle of corporate control of both IBM and Hasselblad is the same - the shareholders appoint the Directors and the Directors control the company. If the shareholders don't like the Directors then a majority, in UK law a 75% majority at an AGM or an EGM, can remove those Directors and appoint different ones. The precise mechanism for so doing may differ according to jurisdiction but the principle is the same. So if DJI have taken a majority shareholding in Hasselblad then that means that, depending upon the Articles of Association of Hasselblad and any weird (i.e divergent) principle of Swedish corporate law, they are in a position to influence and possibly determine the direction the company takes. But it does not mean that they have necessarily invested any money into Hasselblad. I hope they do and I hope that my pre-order of the X1D will be fulfilled soon.
At least according to what I could find, Hasselblad is not a publicly traded company. Most of what is being batted back and forth with respect to shareholders, corporate law, etc. applies to publicly traded companies in the USA. Unless you know Swedish law on privately held companies none of that is relevant.