I just killed the ender dragon in my world and a second egg spawned?

Seems like some sort of bug, as Bedrock Edition has been known to cause strange and glitchy ender dragon behavior, such as an instance where a dragon was able to spawn without needing to revive it because someone went through an end gateway, or an instance where multiple dragons respawned at the same time, so I wouldn't be surprised if this situation is another one of those bugs.

I'd recommend reporting this on the bug-tracker on MineCraft's feedback website; https://bugs.mojang.com/projects/MCPE/issues/MCPE-114956?filter=allopenissues

A side note that I'll also add is that MineCraft Legacy Edition (The discontinued console edition) is the only version of the game that has an intentional game mechanic that you can use to get multiple dragon eggs in a legitimate survival world, as it has a "reset end" option, which when resetted creates a new end dimension with a new dragon that drops the egg when killed.