Reaction of acetylene with hypochlorous acid
The enol probably does tautomerize but it doesn't last. Some of the enol remains in enol form at equilibrium, and that reacts further with the hypochlorous acid.  This causes some of the keto form to revert to the enol, which then gets consumed again by the hypochlorous acid, and so on.  The selective reaction of the acid only with the enol ultimately pulls all of the keto form back to the enol and then the final, fully reacted product you see.