Can cancer be downgraded?

Hi there, I'm looking for advice. Recently I heard that a ex person i know from last year is claiming to have terminal cancer. So they are claiming that they have been diagnosed with stage 4 lymphoma but that after a treatment it was downgraded to 3. They claim to have had chemotherapy 2 weeks before they completed in a sports competition ( they say they have had CAR T cell therapy). They are telling ppl to keep it secret and haven't even told thier family yet. Can they be competing in intense sports activities and other things when the treatments they claim to have would definitely not recommend or even that it would be dangerous to do. Is it real ?