Twyford may well be nursing feelings of resentment about what appears to be punishment for failing to deliver on a KiwiBuild policy that was never realistic, and on light rail, in which he was hampered both by reality and by NZ First.
Ardern will have appreciated that, so there must be other reasons for his demotion.
Those are hopefully more convincing than simply that Twyford had become a laughing stock in the public eye and was associated with failure – a status helped along by National Party leader Judith Collins who once described him as Ardern's biggest liability but Collins' best asset.
It is true that at the public speeches Collins' delivered, she always got a lively response when Twyford's name was mentioned.
Ardern spared Salesa the indignity of saying publicly why she was being dumped, instead saying Salesa's political career was taking her in "different directions" to Cabinet – she would be offered an assistant Speaker role, and potentially a select committee chair.
Salesa is a salutary lesson to Ardern on the risks of putting those without much political experience into ministerial positions.
It has not stopped Ardern taking that risk again, and nor should it. The immediate inclusion of first term MP Ayesha Verrall and second termer Kiri Allan are evidence of that.
But Ardern and her senior Cabinet members now know to keep a close eye on it. They and their staff also have a term of experience under their belts themselves, and can therefore nurse new ministers more effectively.
Both Salesa and Twyford will serve as cautionary tales to ministers that Ardern's "kindness" ethos did not extend to immunity for incompetence or bad judgment. Ardern has also shown she has no appetite for bad treatment of staff.
But Ardern also showed redemption was possible. And she did that in a way that made it clear than those who take their grim fates quietly are more likely to get their second chances.
The restoration of Meka Whaitiri as a minister and David Clark to Cabinet are examples.
Ardern said Whaitiri had "done everything I have asked" and "there should be a place for second chances".
Clark did not even need to be told what to do – he took his resignation as health minister with good grace, knowing well it would stand him in good stead for a recovery.
However, second chances are usually also last chances – and all ministers will now know that.
But by far the most perilous jobs have been given to the ministers who are at the top of their games.
New Justice Minister Kris Faafoi has a difficult job ahead. He will get the task of trying to get cross-party consensus on electoral law changes, including the possibility of moving to a four-year term, and the prickly issue of political donations.
That might look easy given National's leader Judith Collins has said she preferred a four-year term and many parties have been stung by donations scandals.
But Faafoi will quickly find that electoral reform gets very political even when everybody agrees.
Then there is Andrew Little, whose new portfolio of health has long been considered something of a poisoned chalice.
Former PM (and former Health Minister) Helen Clark was among those who sent combined messages of congratulations and commiserations to Little when he was anointed the latest sipper from that chalice. To him falls the fraught job of pushing through the significant reforms bequeathed to him by the Heather Simpson review.
But Little can take some solace in knowing there is now a chalice with even more poison in it. It is the new Covid-19 portfolio, held by Chris Hipkins.
To Hipkins falls the terrifying task of being held accountable for everything to do with Covid-19 – from border management to the health response. A new outbreak? Blame Hipkins. Runaways from quarantine? Blame Hipkins. Christmas cancelled? Blame Hipkins.
Last year, Ardern was repeatedly asked who was ultimately responsible for Covid-19 and she always fudged the answer. Now she has provided it. Poor Hipkins.
