you can't miss bumblefoot as it gets to be a huge swollen mass and the bird is limping. what you posted could just be a callous. I'd just keep an eye on it.
bumblefoot is easy to treat. make an incision in middle of swelling and squeeze out the mass that's inside like popping a huge zit. make sure all the goo is squeezed out then fill cavity w/something like neosporin or other anti-bacterial pintments and wrap in a bandage. remove bandage after about a week.