confusing scope example in ruby

dynamic.rb

# this is the usage that confused me:

# it's a different situation than in your example. i had heard someone mention
# that this worked due to dynamic scoping, but after looking into it, it's actually achieved 
# with reflection. glad we figured this out. hifive! o/ \o

require 'sinatra'

helpers do
	def login
		@user = "test"
		yield
	end
end

# go to http://localhost:4567/, it will return "test"
get "/" do
	login do
		return @user
	end
end