The article says:

  In 2017 a US equity firm TSG Consumer Partners acquired a 22% stake in Brewdog. But unlike the Equity for Punks' "ordinary" shareholders, TSG was given "preference shares". That meant that if Brewdog was sold, TSG was first in the queue to get back its investment plus any return owed, possibly leaving little or nothing for small investors.

It seems the preference shares weren't just 1x liquidation preferences. The 'plus any return owed' was 18% per year if, as I imagine, those shares are the 'C Preferred Shares' described in Brewdog's Companies House filing on 7 Jun 2017. ("Statement of capital following an allotment of shares on 6 April 2017"):

  5 Statement of capital (prescribed particulars of rights attached to shares)
  Class of share
  Preferred C Shares
  Prescribed particulars

  Amount") shall be applied as follows:
  1. an amount shall be distributed among the holders of the Preferred 'C' Ordinary Shares which shall be the greater of:
  a) the Deemed Acquired Price of all Preferred 'C' Ordinary Shares together with, in respect of each Preferred 'C' Ordinary Share an amount equal to 18 per cent of the Deemed Acquired Price per year (based on a 365 day year) accruing daily and compounding annually from the date of issue up to and including the date of the return of capital; and
  b) such amount of the Distribution Amount as would be applied to the holders of the Preferred 'C' Ordinary Shares if they ranked pari passu with 'A' Ordinary Shares and 'B' Ordinary Shares; and
  2. any balance of the Distribution Amount following the application of the amount referred to in (1) above shall be applied to the holders of the 'A' Ordinary Shares and the 'B' Ordinary Shares (in accordance with the terms of the Articles of Association), provided that in the instance that Article 6.2.1(a) applies, the Warrant Shares shall have nil value for the purposes of Article 6.2.2.
  Any return on Preferred 'C' Shares shall be made amongst their holders pro rata as nearly as possible to their respective holdings of Shares of that class.

This may seem like a lot, but it's a common structure for private equity deals, and we have no way of knowing whether that's the best deal that Brewdog's management could have struck at the time.