No idea about other apps, as it was all done purely for fun and for learning purposes, so we didn't really have any interest in potentially implementing the exact same thing but for different apps. Especially since there is no real fun or learning happening when the API just spits out the exact coordinates back at you. To clarify, this was already patched by the time we set our sights on it.
>another one that just sent out coordinates and left the distance finding to the client
That's exactly what Tinder used to do back then, they simply sent out the coordinates and left distance calculations to the client. Given that Tinder (being one of the most popular dating platforms that was also known to be one of the most "tech-forward" ones) did that, I have zero doubt that some other dating platforms could have been using similar methods for determining the distance between users around that time.
>another one that just sent out coordinates and left the distance finding to the client
That's exactly what Tinder used to do back then, they simply sent out the coordinates and left distance calculations to the client. Given that Tinder (being one of the most popular dating platforms that was also known to be one of the most "tech-forward" ones) did that, I have zero doubt that some other dating platforms could have been using similar methods for determining the distance between users around that time.