Strange NPN issue with Python SSL: any protocol is valid...?

odd_npn.py

import ssl
import socket
import certifi

ca_store = certifi.where()
ctx = ssl.create_default_context()
ctx.load_verify_locations(ca_store)

server = "www.twitter.com"

# set a bogus protocol for NPN                                                                             
ctx.set_npn_protocols(['herpderp/7'])
conn = ctx.wrap_socket(socket.socket(socket.AF_INET),server_hostname=server)
conn.connect((server, 443))
# no matching NPN protocol should be returned                                                              
supported_proto = conn.selected_npn_protocol()
if(supported_proto):
  print(server+" NPN sez: "+supported_proto)