So why can't I be Lazy and do this?

Because you're trying to dereference the hash that $obj->method returns, which won't work seeing as how it's already a hash. You could just change your code so that you can dereference your return value e.g

  # assuming $obj->{attr_name} holds a hashref
  return $obj->{attr_name};
}

# code passes

foreach my $item (keys %{ $obj->method() }) {
[download]

My guess is that the hash gets flattened into list context by the return and somehow doesn't get coerced back into a hash by the keys function

A hash is indeed flattened to a list in list context, which is provided by your hash assignment in your second example. However keys expects a % sigil, so while you are returning a hash¹ from $obj->method keys is none the wiser. So you have to enforce the sigil by either using a hash or dereferencing a hashref e.g

my %hash    = qw(foo bar baz quux);
my $hashref = \%hash;
my @list    = qw(ichi ni san shi);
my $lisref  = \@list;
 
keys %hash;          # valid
keys %$hashref;      # valid
keys %{{@list}};     # valid
keys %{{@$listref}}; # valid
keys $hashref;       # invalid
keys %{@list};       # invalid
[download]

HTH

_________
broquaint

update: added further clarification about hashes
¹ you're not really returning a hash, just a list which is being stuffed into a hash

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