And it was explained to you, very clearly, that that was because they were exposed to radioactive materials, which can be very harmful if any tiny bits get into your body, like if you inhale a dust sized grain, or a tiny fragment gets on your hand and then you eat something and ingest it. Being exposed to ionizing radiation is completely different.
By the way, if they were exposed to those samples as students, as you said, it's extremely unlikely that they were working with anything radioactive enough to cause any health problems, at any point in their lives.