They announced a sales record where the metric is "sold to somebody that never ever had a mac before" combined with "in the first week of availability". The headline is worse than Cook's tweet quoted in the article.

To get this record you need to have a long time were your costumers were buying something else from you (like Phones) and have a lot available inventory in a lot of places in the first week combined with a great media coverage. 3 things that Apple has an advantage in.

As @ibero above points out it is more important for apple to tap into the vast demographic of relatively young iPhone/iPad customers - the older Mac customers are buying different machines.