Paul Oter wrote:
If you interchange with the DLR at Bank you need to touch your Oyster
card flat on the yellow reader again on the DLR concourse. If you do
not touch in and out at Bank's DLR concourse you may be charged more
than you need. This is not necessary at other interchange stations."

Which suggests that you *do* need to touch out at the DLR concourse,
though it isn't clear whether you still need to do it if you intend to
exit Bank station though the ticket gates immediately afterwards
(obviously you need to do it if you are using the lift to King William
Street).

If the question is really "did the passenger go through zone 1" then
the same could be the case for other journeys where the user may have
gone on Silverlink:

1. Highbury & Islington to Canary Wharf (DLR): Passenger may have
changed at Stratford or may have gone down to Moorgate on
FirstCapitalConnect then Northern Line to bank then DLR (from
experience this is the quicker route).

2. West Brompton to Stratford (not Jubilee). Could go via Silverlink
all the way changing at Willesden Junction or could take District Line
changing at Mile End.