Agreed, could be nothing, but at least they will be aware of it if there is any relevance.
I've got many years experience in the CJS and I struggle to believe that a PO tasked with securing CCTV in London would need to call a MOP to find out how to access TFL CCTV.
I looked at it more that they're curious that a site not owned by TFL is storing the stills... In an innocent - What is this vibe.