What Causes Contact Bleeding?

my sister is 35 years old. she did a routine pap smear test today and the doctor said that he found some contact bleeding. he said it could be that she is clearing out from her period which she got 9 days ago. when she asked what it could be he told her that they shouldn't worry for now and wait for the results. if anything, he would send her to a specialist. he seemed somewhat in a hurry to get the test checked however. what could this blood mean? is it serious? thank you