The 3x100 kg bombs for the Po-2 can unlock in 2 possible ways:
- Win 1 online CTA games
- Win 2 online games
So my guess is that you simply unlocked it by winning 2 games.
Several aircraft/loadouts can be unlocked in 2 different ways, the list here (link) should contain all the information if something can be unlocked in multiple ways. It's impossible that your game would be more glitched than that of others, so you most likely simply unlocked it using the alternative way.