No idea, it's been years since I last worked on it. It was also not the only Go service written at Apple (90% of cloud services at Apple were written in Java), though it may have been the first one used in production.
Apple's server stack has been primarily Java for about 20 years.
Great use case for Go though, especially its concurrency features for web crawlers. I reckon Scala could work too, although it's a lot more complicated / clever.