I've searched the internet, and found some more information for you.
The pictures at Filton Abbey Wood were commissioned by the Severnside Community Rail Partnership in 2022. They're given the title "Pioneers of the Railway" and celebrate individuals from under-represented backgrounds who have strived for progress and made a difference on the railways. Here's a link to the website:
Emerging artist Valentia Huxley has been commissioned by Severnside Community Rail Partnership to create a series of portraits for Filton Abbey Wood Station. These vibrant works celebrate individuals from under- represented backgrounds who have strived for progress and made a difference on the...
severnside-rail.org.uk
It doesn't specifically mention Black History Month, though.
Those at Gloucester, though, were for Black History Month in 2023. They were commissioned by the Gloucestershire Community Rail Partnership and showcase images of individuals from the county's black community.
The full story is here:
https://www.gloucestershirelive.co....k-history-month-exhibition-gloucester-8875892
As well as Gloucester, there were (or still are, I'm not sure) exhibitions at Stroud, Stonehouse and Cam & Dursley stations.