Would having mono 5 years ago cause a blood test to show possibility of autoimmune liver disease today?

No. In fact, if you have labs suggesting autoimmune hepatitis, i would be very concerned and would be hammering away at my doctor for all the information i could get. It is possible that an old hepatitis (infectious mono, hepatitis a) may trigger autoimmune hepatitis -- the jury's out on this, but it's moot. Please comply with your diagnosis and if needed treatment, and enjoy a long healthy life.