The code would have looked just as correct and would have been just as wrong with the "old" non-sigil `try!(...)` syntax.
Based upon the way the code was written, it was, at least in the mind of the author. They forgot they could exit scope there. They clearly didn't _intend_ for that outcome, but ended up with it anyways, possibly out of habit, and possibly because a single impactful sigil like that is easy to miss in review.
I get that technically it didn't cause the memory leak.. but just look at the way that was written initially... it obviously led to it _within_ that particular structure.
Their mistake was writing resource management code that requires manually thinking about where they might exit scope.
I do not know what metric you use to define "better"
In Rust, I think you only really run into this issue when interacting with C (or otherwise engaging in unsafe code), so for normal Rust coding it doesn't need to be spelled out as a guideline. And the Rustonomicon[2], the go-to resource for unsafe Rust, isn't really written as a set of guidelines. At least from a brief search, I found it harder to find a Rust page that specifically says "don't do this".
1: E.g. https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines..., the first guideline in the "resource management" section.