Vince has the right answer. The syntax you see is the result of using multiple trailing closures. It's great that you see this and are asking questions. We see the gears working in your head to make sense of SwiftUI. Nice!
Usually I might derive some car, or house-based example to help clarify this concept. But at this point in your development, you might want to know that when Swift was first released, trailing closure syntax was available, but only if the LAST parameter in a function's signature was itself a function.
From the start, developers wanted more! Why not have multiple trailing closures?
One of the ways that Swift evolves is for the Swift community to propose changes. These changes include detailed proposals and examples on how new syntax might work, and of course includes a wonderful essay on the many benefits to humanity.
Other developers get to weigh in and give their thoughts as to why the proposal is complete rubbish, and would produce rabid code devils that would plague humans forever.
Some proposals die a long and painful death. Your new friend Multiple Trailing Closures survived the ordeal!
Take a look at this github repository for some of the juicy details and comments.
Proposal: Multiple Trailing Closures