Except that in Go, you always return the error alongside the value, like this:
return 0, errors.New("unable to get price")
You've missed the problem that was posed. It wasn't returning 0 to indicate an error, it was changing the error value from nil to 0. In rust that would've been a type change (from Option<int> to int). Because the context here was about how stronger type systems (like rust's) allow you to be more specific about your types, and thus many code changes that would not involve the type changing in other more weakly-type languages do cause a type change in rust.