I find it hard to comprehend how sort can "see outside" of the foreach loop.

That's common for all blocks.

my $var = "Hi!";
{
   print("$var\n");
}
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my $var = "Hi!";
for (1..2) {
   print("$var\n");
}
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my $var = "Hi!";
print(map { "$var\n" } 1..2);
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my $var = "Hi!";
sub func {
   print("$var\n");
}
func();
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Yes, the following works even though $var goes out of scope before func is called.

{
   my $var = "Hi!";
   sub func {
      print("$var\n");
   }
}

func();
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