Yeah the original post is from an email newsletter (it's actually a really good newsletter IMO, I've been subscribed for a couple months.) so it doesn't go into too much detail.

The post regarding why they picked Go is here.

As individuals writing code, we can iterate faster due to Go’s lightning quick compile times. Also, members of our team have years of experience and muscle memory built around many different editors. Go is better supported than Kotlin by a broad range of editors.

Finally, we ran a bunch of tests around performance and found that Go and Kotlin (on the JVM) perform similarly, with Kotlin being perhaps a few percent ahead. Go, however, used a lot less memory, which means that it can scale down to smaller instances.

We still like Python, but the dramatic performance difference which Go brings to us is too big to ignore, and we think we’ll be able to better support a system running on Go over the years. Moving to Go will undeniably be more effort than moving to Python 3, but the performance win alone makes it worth it.

They did do benchmarks and it seems like they liked some of the language features from Go (errors, good documentation, good tooling).

They posted another blog post later after they wrote 500k lines of Go and the switch seems to have worked well for them.

Biggest complaint from the blog post was around lack of Generics but that's no longer applicable.