Gragas Barrel slow interaction with Tibbers (when on same team)

In ARAM while playing as Annie when I have Tibbers on the field and move far enough away from him to force him to TP to me and Gragas detonates a barrel from his Q at the same time with Tibbers in the AOE when Tibbers appears beside me both him and me (Annie) are slowed. The popping sound is also made like the barrel was beside me when it went off even though it is at the original location. The slow VX is also displayed on both Annie and Tibbers. Tested twice and was able to duplicate.