"A friend and I set camera to capture fruit bats rising from Botanic Gardens. This was a big surprise," he tweeted on Wednesday.
Crowe provided a link to the footage, which was posted online late on Tuesday from a brand-new account by the name of ParallelUniverse1234. It's unclear if the account is run by the actor.
The short clip titled UFO? Time Lapse Photos Outside RC's Woolloomooloo Office (THESE ARE REAL) shows a number of oddly-shaped lights over what appears to be the Botanical Gardens.
The actor defended the video's veracity when asked if the lights may have been lens flares or other natural phenomenon.
"Canon 5D, no flash, can't be lense (sic) flare because it moves, camera is fixed," he replied to one Twitter user.
"The camera is on a balcony - not behind glass."
He said he was about 250 metres from the gardens when he caught the footage.
It remains unclear exactly what the objects are - if anything - or whether little green men are visiting Sydney.
Social media users cast instant doubt on the footage.
One person commented on YouTube: "Common RC. It could have been more believable without all the editing. Just raw footage would have made it viral. Anyways, loved you in Les Mis."
Another added: "Russell Crowe - are you not entertained!" referencing one of the actor's famous lines in Gladiator.
In earlier tweets, Crowe was lamenting the low-key publicity for his new film Broken City.
So he may be simply trying to drum up a little buzz.
Maybe we'll never now.
But the truth is out there.