What is a level 4 carcinogen?
There are several different ways to rate carcinogens.  According to its MSDS, Pyridine belongs to Group 3, A3:  Known to cause cancer in animals, inadequate evidence in humans.

If it was just contact with the skin, your friend should wash it off with soap and water immediately for 15 minutes (this is again from the MSDS).  Short term exposure can cause "irritation (possibly severe), allergic reactions, sensitivity to light."

So, if any irritation occurs, it is probably not serious, but I would recommend seeing a doctor anyways.  I doubt there is anything to worry about, but cancer is not something to mess around with.