My only guess as to what happened is that he either was literally applying suction to the labia and for such a long period or so repeatedly that there was a build up of fluid edema; or he bit it, bumped it with his chin or hand or caused some abrasion injury; resulting in inflammation. For it to happen so suddenly and only after oral sex I can't imagine it being anything other than minor swelling, it should go away in a few hours.
The same thing happened to me today. Did it go away?
Just one lip is swollen and the skin covering the Clit.