He said that when sado wanted to get stronger, so he told renji to train with him, then renji said why don't you do it? Uruhara then replied saying he is just a lowly shopkeeper ( joke ensues), after that renji says they all know he used to be a captain, so he had to have bankai.
It's then when Uruhara said that his bankai isn't the type that can train other people.

Seems obvious, since the shikai dispatched of yami quite easily, also he canceled out yami's punch simply by using the same amount of force. But it didn't seem he was having a hard time at all when doing that.
So yeah, Uruhara is epicly strong.