Swift Cross-actor references and Sendable types

In proposal paper for the Swift language's actor model here, it's not allowed to call function returning non-Sendable type across actors.

However, I tried the example in the paper and it can compile and run while it suppose to emit errors.

class Person: CustomStringConvertible {
  var name: String = ""

  var description: String {
    return "Person name: \(name)"
  }
}

actor BankAccount {
  var owners: [Person] = [Person()]

  func primaryOwner() -> Person? {
    return owners.first
  }
}

@main
struct EntryPoint {
  static func main() async {
    let account = BankAccount()
    if let owner = await account.primaryOwner() {
      owner.name = "FooBar" // Change actor's mutable state outside of actor-isolated context
    }
    print(await account.owners)
  }
}

// Output: [Person name: FooBar]

My Swift version

$ swift --version
Swift version 5.5.1 (swift-5.5.1-RELEASE)
Target: x86_64-unknown-linux-gnu

Did I do something wrong in the code above? If I did it right, why the implementation does not conform with the proposal paper?

Thanks.