It was indeed; it was proposed and implemented by engineers working on the Swift For TensorFlow project. The earlier dynamic callable features were as well, in order to offer Python interop.
Re:What’s New in Swift 5.2
by edflsafoiewq on Thursday February 06, 2020 @02:02PM
(#22259114)
It's just C++'s operator(), right?
Chances also are that it is inspired by python’s callable (https://en.wikipedia.org/wiki/Callable_object#In_Python), which, as far as I know, people don’t complain about much.