Let me see if I can explain...You can get stabbed with a pencil lead in, lets say, the forearm. FIVE YEARS LATER, all of the sudden, develop a lesion/bump (like what you have had). THIS IS BECAUSE....Your body, in particular, your "crime fighting" cells, recognize that something different is here. Then, they all gang up (like a high school fight with so many ppl surrounding) and isolate what they recognize to be foreign. (in the example, it would be pencil lead; in the biopsy of the compound nevus~ it could be part of skin left, some bacteria introduce when a sterile field was broken, etc. Then they fight. It is important to let all drain out.
Didn't you say you squeezed the "pus" out? The deep whole is from the cells isolating that foreign infection, etc. That is why it is called a DEEP CLOSED SKIN WOUND. In addition, abscess are not on the surface of the skin.
You need an MRSA defensive abx! Please, please contact your local care provider for that!