Heck I just played last night....
your party must have had a run of horrid luck...
lets see, all the goblins need to roll against the passive perception of all the pre-gens, of the the heroes (the halfling I think) has a 15 or 16...
the goblins have a +3 stealth...I may be wrong on this one.. but lets say they have +3
you rolls for all of them. against all the players... you roll'd 10+ on every die roll.. (the cleric I was playing had a passive perception of 13)
then the combat started...
I know my dwarf had an AC of 18 (with 11 Hp), one of the fighters has 17
so here, with their mighty +3 to hit, you rolled 14+ to 15+
I think there are 6 or so goblins....
d6+2 damage for short bows?
my cleric had 11 HP, so unless you rolled a critical, one hit will not drop me.. the fighter had more HP 12, the wizard has 8
so you rolled almost max damage on some attacks and rolled a critical on everyone over 8hp.
Guess what, I can TPK a party with rolls like that in 1st, 2nd, 3rd, and 5th edition..... (not talking about 4th, where death was NEVER a threat for the time I played..like ever)
Yeah; you would have had super ridiculous luck on both ends in order to win with that fight, even with a surprise round. This sounds like insane luck on one end as well as terrible initiative rolling & damage rolling from the PC end.