Hello, thanks for asking your question!
You mentioned the molar was extracted a while ago.
Obviously, if you are for some reason perhaps overly concerned, you could always get an x-ray taken of the area by your Dentist
of preference to ascertain with more conclusiveness. But, the "most probable" reason for the hard bony lump is something that happens actually fairly regularly after an extraction - where the bone heals, but NOT entirely smoothed out.
In other words, it is more than likely bone. Just hasn't healed 100% smooth, which understandably you would wish it would. But, it fortunately NEVER will cause you any trouble, for the most point, so these bony spurs (hard bony lumps), are often best left alone. You could always have the Dentist numb you, and smooth the bone down & suture it and it would then heal smooth, but it would not, my opinion, be worth the time or hassle or expense.
So, it is something to likely not be concerned about, and yes, it happens fairly regularly after an extraction! I hope this helps you.
If you have any further concerns/questions, don't hesitate - OK?