I always find it amusing when you sign up for a service, and then for the next little while, half the ads you see are for that service. "Uh... but I've already signed up..."
I think I learned in my marketing course that we (statistically) tend to look out for ads for things we have bought after the purchase.
The reason is hypothesised to be because our brain is actively seeking confirmation of previous decisions.
That said, your case most definitely was because of indiscriminate retargeting. Also I guess the effect I mentioned is more visible for bigger purchases : )
