Why do rspec filter hooks only work with arrow syntax?

In RSpec tests, I'm using hooks/flags to run subsets of tests, similar to what is shown in the examples

# spec_helper.rb
RSpec.configure do |c|
  c.filter_run_excluding('broken')
end

This syntax works

# my_spec.rb
describe 'broken test', 'broken' => true do
  ...
end

This syntax fails with error syntax error, unexpected ':', expecting end-of-input

# my_spec.rb
describe 'broken test', 'broken': true do
  ...
end

What is the difference between them which causes one to work and the other to fail?