Syntax is ultimately a fairly minor aspect of languages. The reference and value semantics, the memory management, the type system, the language runtime, these are what really create a development experience in a particular language. And they are on nearly opposite sides of the spectrum between Swift and JavaScript. If you are only superficially doing something in the language, a somewhat trivial project or just experimenting, then they might seem more similar than they really are.
> C-likes also don't often have first-class functions/closures
I think C is the only remaining C-like language not to have first-class functions. And there are compiler extensions for that too.
My understanding is that in cases like Java and C++, the lambdas aren't truly first-class; they come with limitations. I could be wrong.
The array/dictionary literal syntax (especially dictionaries) was probably the main thing. Lots of languages have similar array syntax (though fewer have the auto-grow behavior), but I can't think of another C-like language with first-class, dedicated dictionary syntax.
C-likes also don't often have first-class functions/closures, or named function parameters (JS doesn't technically have the latter, but it effectively does with object destructuring; this is one of the syntax niceties Swift added).
I didn't mean to imply they had an overall similar set of features, so much that someone who's comfortable with TypeScript would have a pretty easy time warming up to Swift, which matters on the web.