usage - "You're reading this because..[reason]..aren't you."

I came across an image of a toilet cleaning product, which had the following printed on the label:

You're reading this because you forgot your smartphone when you went to the toilet didn't you

Forgiving the lack of punctuation, someone on the online forum pointed out that the correct format would be "aren't you", not "didn't you".

To me, both make sense, as you could be referring to the first part of the sentence ("you're reading"), or the middle part ("you forgot").
Could they both be appropriate?