Not sure if this was a glitch but walking away from anises cabin a swarm of bats passed by me from the path heading towards riverwood. I'm on xbox and I have never seen this in 2 years. Was it a glitch from nearby bleak falls or have they always been seen outside

Random encounter added by the Dawnguard DLC.

Are they the bats you normally see once across the bridge from Riverwood? If so, I have seen those in every playthrough I can recall.

As ShadowTitan said above, it is a random encounter (added by the Dawnguard DLC). There is a random encounter spawn point near Anise's Cabin, so this isn't a bug. The bats that you see near the bridge at Riverwood or in certain dungeons (like the final room in Bleak Falls Barrow) are completely different and are not random encounter related.