I'm not the original comment author, neither am I fluent in Perl. But I suspect they meant nested hashes and not a hash whose values are arrays of arrays. As you point out, the latter is trivial.
To be clear, even a nested hash is all well as long as the depth and the keys are literals (as in your example). It is when keys are dynamic that things get unruly. And god forbid if the _depth_ of nesting is dynamic. All of these are trivial to implement in Python, Ruby, JS, PHP, ...
This is why we use strict! The extra arrow is unneeded, as you're working on the actual hash, not a reference to the hash. This is a compiler error with use strict though, so it's not something you would generally be bitten with when writing real code, just internet comments. :)
I think the point is not that Perl's rules don't make sense -- it's that they're much less obvious than those in many competing languages. In Python, lists are `l = [1, 2, 3]` and dicts are `d = {"key": val}`. Both structures can be nested without any change to the semantics.
To be clear, even a nested hash is all well as long as the depth and the keys are literals (as in your example). It is when keys are dynamic that things get unruly. And god forbid if the _depth_ of nesting is dynamic. All of these are trivial to implement in Python, Ruby, JS, PHP, ...