Since there was alot of bots in league IV more than one team in your conference went up. And those two teams went up because one of them won the finals and the other had a better record than you.
Actually, based on his record (20-2 and conference winner), I would guess there weren't a lot of bots in league IV last season. Here's the order of preference from BB-Charles for determining who gets promoted to replace bots:
(158664.3). Based on the fact that he didn't promote, it means you had to at least win your conference, finish with a 20-2 record, and a better than 365 PD to bot-promote out of DV.