hi and welcome ,
Entrapment of air in the extraction socket is a rare condition , because after extracton of wisdom tooth the socket is curretted to remove all the irritants and compressed which helps in clot formation and faster healing.
Though we can expect air embolus to be formed in the jaw bone which leads to pain or as you have mentioned the swelling feels hard it may be a bony spicule or remnant of alveolar bone left unfiled.
i would suggest you to get a X RAY
done for the affected area which will show the cause of swelling accordingly your dentist
can plan the treatment for you .
i hope this information helps ,