Ryze Ult into Enemy Fountain

In my game last night my friend Ryze ulted me into the enemy fountain (thinking it would kill me) but instead of me being targeted immediately by the fountain it didnt notice I was there. I stood in the enemy fountain for about 5 or seconds before the enemy team attacked me then the fountain targeted me. I dont know if this is a bug or just a one time thing. So I'd like to have some feedback about this from anyone! thank you