Their video shows you moving quite briskly round the back of a reversing car, not slowing down at all; its as if the signs aren't there as far as you are concerned. Was your husband not aware of the meaning of the "FLying Motorbike" signs that he passed ? They mean "No Entry for road vehicles" The signs sometimes have the applicable hours and days of the week for the restriction, and sometimes a sign below with other exceptions like permit holders etc.
Looking at GSV (latest date Dec 2020) on Mount Stewart Avenue going west shows this advance warning sign : -
https://maps.app.goo.gl/YHJEn5BQK8GitJ157Then, as one approaches the restriction, the sign, which has exemptions for BB holders, Commercial deliveries and permit holders. Bear in mind this is 2020. There are no later GSV views, so we don't know if the sign has changed since then.
Are you or your husband a BB holder, because this is one of the exemptions on the sign ? However, the current sign is slightly different on ther photos, but it is unzoomable, but I don't think BB holders are exempt anymore, but I may be wrong. Only you can tell us what the sign says now, as GSV is 5 years out-of-date.
It may be well worth submitting reps anyway, but best if you can claim an exemption which guarantees cancellation.
