They picked Go after meaningfully considering Rust (and others). I don't remember all the reasons for it but it was detailed in the original blog post.
There's the blog post (by Anders Hejlsberg, the author of Turbo Pascal, chief architect of Delphi, currently lead architect of C# and a core developer of TS; I'd say he knows his languages), but they also posted FAQs, here's some good reads:
The blog post: https://devblogs.microsoft.com/typescript/typescript-native-...
Why Go? https://github.com/microsoft/typescript-go/discussions/411
Why a port instead of a rewrite? https://github.com/microsoft/typescript-go/discussions/410