It could be related to the sore throat, but it could also be a simple cyst. There are hundreds of kinds of cysts and they're not dangerous except that they can get infected. One other thing to check for is whether or not the lump is moveable (feels like it's rolling around under the skin when you rub it) or if it feels like it's anchored to the tissue. Most cysts are hard like you described and have that moveable feel to them.
Because the lump is located in an area so close to the lymph nodes though, it would be a good idea to have a doctor check it out. It's probably nothing to worrry about, but any kind of lump in that area should be looked at by a doctor.