Why does whatsmyip.org return a IPv4 address on phone and IPv6 on Surface?

When user checks the ip address using whatismyip.org using a cell phone browser (On Blackberry 10) they get an IPv4 address.
But when they check using their Surface, they get an IPv6 address.

Is this indicative of any networking problem?

They got same results from two different Wireless networks, each WLAN connected to a different cable modem/router.

Thanks.