He probably doesn't take very long to display his art because it's stenciled and someone with high vis, cherry picker working at night isn't unusual in many places, but it is surprising that there doesn't seem to be people with CCTV/ring doorbell footage of him (or maybe there is, I haven't googled).
The BBC did an interesting podcast series about him about a year ago:
https://www.bbc.co.uk/sounds/brand/m001nwhs