Can someone explain to me what this is?

It happens sometimes but I don't know the reason why. It's a simple fix though - just swap the buddy to something else and then back to Lotad.

Just keep walking. When you hit the next candy distance it resets. In your instance, you’ve walked 0.3 km and it’s showing the distance til your next candy.

you have received two candy instead of one. If you swap buddy and place it again it will reset to 0 and you will be a candy ahead without walking the 3 kilometers needed for it.

It’s not a bug, it’s award for you. Free candy every 3 kilometers.