The timespan wasn't a surprise. Vergil is well aware of how long demons can live, and of legends back then of a witch named Eva and her contract, Sparda. He wasn't stupid enough to think it was a coincidence.

"So you disobeyed your master, and found yourself caught in the repercussions."

...what was Alastor expecting, a thank you?

"Will you do the same to Dante?"