to answer your question pretty much anything thats rendered on your screen inncorrectly ( whether caused by a driver error, heat issue, faulty card, ect.) is an artifact.
the pressence of an artifact just means something isnt right. it might be fixable and it might not be.
you could have a driver problem, but from what you have said in your post you definaly have a heat issue and that should be fixed reguardless or you will defianlty have perment damage. if you suspect that it could also be a driver issue then you should remove your drivers, use a driver cleaner (I personally have used Nasty File Remover for a while now and its always worked fine for me.) and reinstall your drivers.