I think you need to understand the process behind actually building the car. The factory will have a build sheet that specifies every single part on the car. If that build sheet calls out gloss black surrounds, either deliberately or inadvertantly, then that's what the car will get.I just don’t get how a UK spec car had them fitted from factory when we can’t order them.
Now, it may be that this was a mistake in the factory (as with DSG FRs being fitted with steering wheels without paddles) or it could have been due to the factory changing over from grey surrounds to gloss black ones (in advance of the MY19 changeover) due to a lack of stock.
Not every part of the car is subject to an option. For example, few of the people getting there cars now would have expected DSG7 gearboves at the time of odering. I guess the same thing happened with MIB1 / MIB2 entertainments units.