The Legend of Korra

I don't think it's too big of a jump. Remember Boomy from the original avatar? he could Earth bend with his eyes. I don't see this as a huge jump, especially since many of the white lotus during the Last Airbender were very powerful people as well.

Bumi was only Earthbending small rocks with his face. It's not like he did all that Earthbending from his cage.

Also, we've seen characters like Bumi showing the ability to bend that many rocks, however we've never seen a Water Bender bend not only that much water, but that much water plus the resistance the human body would create from Bloodbending; especially not at night, and especially not during a full moon, both of which increase a Waterbender's power.