I think it was a little of both.
The attack on Dunkirk was halted for several days. I think, in part because Hitler had never wanted war with the UK and admired them. It was Hitler who ordered the battle halted, and then resumed.
It is very conflicted. At any rate, the Germans stopped the attack for three days and allowed a defensive perimeter to be established and the evacuation to be organized, allowing something of around 338,000 allied troops to escape. The entire battle lasted 11 days and it was the French defense that allowed the British time to evacuate, as well as that three day pause in the battle. Had the attack been pressed it would have been an even greater disaster for them.
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