Teleporting Nunu bug/expolit?

Was playing mid lane vs Jayce with an enemy Nunu Jg. Was laning normally when all of a sudden Nunu appears in lane and stuns me with Biggest snowball ever. I was very surprised, but at first left it up to me having my camera positioned poorly and not seeing it coming. When watching replay recording however, you can see Nunu in his botside jg and then teleporting suddenly into midlane. Is this a bug? If anyone has insight into what happened here please let me know.