While true, the BBC has always taken current popular media as a platform to have a frank discussion about the issues that media explores. It's not intended to advertise the film, so much as expand on the events portrayed for those who came out of the film wanting to know more.
The politics were involved, but in a subtler way, by warping the decision-making process. The army was exhausted and needed to rest, repair their vehicles, and resupply. There was debate about whether it should first finish off the Dunkirk pocket or let the air force finish them off, and the air force chief Göring (who was both politically strong and fantastically overconfident) insisted that he could take care of it. Very similar to his later overconfidence in the Battle of Britain, and the way it warped German strategic decision-making.
(Currently considering whether I should Britsplain Dunkirk and its significance to HN. Any takers?)