Any good creature will defend itself, certainly, but think about the context: an adult gold dragon against a party which, even if suspicious and untrusting, it really shouldn't consider a threat. Until they acted in such a way as to show they were a threat, it should be supremely confident in its ability to defeat them at any point.
(Metagaming, we know this is a party of 4th or 5th level PCs IIRC against a CR 17 creature... this should not have even been played out IMO and simply narrated by the DM. It is like when a high-level party encounters a dozen kobolds--the result is pretty much indisputable... why bother wasting game time resolving it except to give the players a "power-high" as they crush kobolds. Just narrate the encounter. So, what the DM felt it was necessary to give the dragon a power-high by crushing the PCs?)
Even if angry, it would LAUGH at the drow's feeble attempt. It also knows much of the party is cowed by his dragon fear and another is pleading with it again. So, the player rolled another 1... and the DM decided that was really the "one roll" that would seal the party's fate.
It is a pity, IMO, that a game where people enjoyed their characters and had fun, would end because of a roll, when the threat the party represented was negligible. It could have been handled in SO many other ways which would have been just as much fun (if not more) and not led to a TPK.