According to the diff, the pool factory should be the closest to the truth.
Me, and others pools are using the getmininginfo return, who says
"netmhashps" : 293.35217118,
I think it's more a display error.
I'm running several HBN daemons, and they all says the same hash.
I think getmininginfo should be the correct way to get the network hash rate. All pools (plus my client) are showing the same rate, except theblocksfactory.