Very well, in agreeing with those three items we set a 400 year period in which something happened that caused this fringe group to form and become the official religion of the Roman Empire. This apparently began very soon after the time of the crucifixion. Once again, extra biblical sources are extant that show mention of Jesus and his teachings as early as 30 years after his death. Flavius Josephus and Thallus both mention him and Thallus even attempts to explain away the darkness that occurred immediately after Christ's crucifixion. Here the Biblical account of a miracle is in agreement with extra-biblical accounts saying "Yes it happened, but it wasn't a miracle". Whether or not it was a miracle is of less importance than the agreement that it actually occurred. This lends credence to the rest of the story. Certainly an author can begin relating a story factually and then go off on a fictional tangent, but at least to this point we have corroboration that things happened the way that the Gospels describe them. Whether this was the work of God or not is a matter of faith.
Now let's look at possible reasons we could have this corroboration:
A) The author is trying to refute a real event. That is Thallus has heard the accounts of Jesus being crucified and puts forth another interpretation of the facts.
B) The author is responding to a fictional account of the crucifixion. Why explain it away at all? If it didn't occur, find somebody who was alive at the time and ask him. A solar eclipse, coupled with an earthquake and accounts of the dead rising is not something that the populace is likely to forget. 50 A.D. is becoming a stretch, but even in those days living to sixty or seventy wasn't unheard of. There should have been somebody around to refute the occurrence. In my forties, right now, I can relate the story of a solar eclipse that happened on my 16th birthday. I'm fairly confident that I can also relate that I’ve witnessed no total eclipses in this locale during my lifetime. I see no reason why this would not be the case for 1st century man.
If A is correct, then we need answer no further questions. An eclipse happened at precisely the time that a historical text said it did. Great, the text seems to be accurate.
If B is correct then we have a few questions to answer:
Why refute it at all? (certainly, the reason would be that a lot of people were running around saying it happened, good enough reason to refute it)
If it didn't happen, why didn't Thallus produce some evidence that it didn't happen in the form of witnesses to that effect. There could certainly have been some people around who could answer whether the darkness and earthquake occurred. We are left only with Thallus agreeing that there was darkness and an earthquake, and no evidence to refute that agreement. Therefore it is likely that the earthquake and darkness actually occurred around the crucifixion, at least there is no sound basis for questioning the biblical and extra-biblical accounts as they agree.