[GAMEPLAY] blue buff and xp given to wrong champion

Okay, so the weirdest thing happened in a game today. I was playing eve, and tristana and vayne (I know, bad) were helping me start blue buff. At just over half health they both left, I continued fighting it, smited just a little early and finished with an auto attack.

Then I noticed I gained no experience whatsoever, and didn't get the blue buff. I looked at the adcs, who were already in Lane, and vayne had the blue buff on her. I mean if it was tristana I'd think maybe her DOT took the kill, but vayne doesn't have any DOT does she? It completely screwed me as I was still level 1 with no xp, could barely kill wolves before basing at 1, etc... (I was still 3 when solo laners hit 6). I just want to know what the hell happened... vayne was already in Lane and the blue buff magically appears on her and it looked like her and tristana shared the xp and I got none, even though I was the only person at the Camp. Was this a bug or is this explainable?