This is dead fat too close to the skin, which lost enough local circulation for tiny dead skin openings to form, allowing the liquefied (dead) fat to drain.
Even done properly, BBL requires transplanted fat to be surrounded by adequate blood supply to heal and ultimately survive to preserve...
Infections are fairly rare after BBL if done by a qualified, board certified or board eligible plastic surgeon in an accredited facility- usually less than 1% risk. The cellulitis they saw on the CT scan may have actually been localized inflammation after undergoing the procedure....
Based on the photos that you have provided it does appear more like an infection/abscess. However, an in person exam would be needed. Continue antibiotics and follow up with your plastic surgeon regularly. If you should have any changes to the area contact your surgeon. Best wishes.
