Someone noted the UK position required shareholder assent, which sounds like what you're saying here.
If shareholders vote that sounds 'fair'. If the board decided and shareholders are obliged to go with it as that's how shares are [in some particular jurisdiction/market] then it being fair seems of no concern to that system (as a sibling content intimated).
The board basically voted to stop standing in the way of the deal and submit it to shareholders themselves since they confirmed that A) it seems like an ok deal and B) it's likely to not waste everyone's time.
In this case, Reuters reported here https://www.reuters.com/technology/exclusive-twitter-set-acc... that the deal is subject to shareholders vote before it can be closed.