Edit: my mind might been blurred by too many 4s and 6es, whoops. I thought it said "6 IPv6 addresses". This still doesn't explain why it's six though, although

Edit: my mind might been blurred by too many 4s and 6es, whoops. I thought it said "6 IPv6 addresses". This still doesn't explain why it's six though, although I can think of four simultaneous IPv6 addresses - transient and persistent GUAs (which are accessible to the internet) a ULA (equivalent to IPv4 private address but which is rare in practice) and a link-local address (for communication to the router).