I've encountered this as well, and I think it's somewhat inconsistent with current Swift which does not allow to call a function with a single tuple that contains its arguments anymore (swift-evolution/0029-remove-implicit-tuple-splat.md at master · apple/swift-evolution · GitHub).
Possibly, we are just in a very long transition phase, and there are some rough edges regarding tuples (see Roadmap for and state of single element tuple types? or The Generics Manifesto and single-element tuples for another example).