can windows users learn SWIFT?

Answer 1

Why not?
there are online tutorials and compilers .
you can install Mac Os on VM like VmWare and start deveolping Iphone apps, will need Mac device to publish it.

Answer 2

yes they can, there are online Swift playground websites you can use to practice and learn. one of them is http://www.runswiftlang.com/

Answer 3

https://www.youtube.com/watch?v=o43UuseWIWM

Check this video.