Bumblefoot starts as a wound on the foot, and when bacteria, usually staph, colonizes it and infection sets in, the wound develops a black scab with a pus plug underneath.
Your photos show swelling signalling a possible foot injury but not bumblefoot. Soaking in warm Epsom salt can help heal it, and spraying the foot with Vetericyn may also help.
You might examine the foot more closely for signs of a thorn or sliver that may have embedded in the foot tissue and now has become all but invisible due to the tissue swelling around it. The warm soaks may help reveal it.