Author here: They are unrelated.

We did take the time to examine writing our own full search engine based on Lucene, like the aforementioned search library. The reasons why we didn't are briefly mentioned in the blog post, but simply put, we found Lucene too bloated for our purposes (intended for large-scale data retrievals, among many other things). We just needed a low-cost search over a relatively small dictionary, which could be used in an auto-complete field without stealing resources from other processes, such as our recommendation engine.

I thought the same and was going to mention something. Seeing 'Ferret' alongside search brought up bad experiences with that Ruby library.

But it looks like this Go library is not based on Lucene which the Ruby version one was and I don't think that Ruby version is maintained anymore so maybe it's not a problem to have the same name.