Not being there and not having access to BA staff present to ask them, we can only hypothesise, but perhaps-
Delay/Cancellation caused flight to be overbooked.
Operational decision taken whilst on airport control literally minutes before boarding means last row of CE downgraded to Y to accommodate 2 additional pax (4 to 6 in row).
OP and travelling companion queue in boarding group, gate staff aware that 2 people with Asian names were in last row and therefore (or ? by Fly or is it just for upgrades) they knew OP and travel companion has been downgraded, but also downgrade hasn’t been actioned yet.
Gaye staff ask OP and companion to step aside to ensure boarding continues and already delayed departure isn’t further delayed whilst the downgrade is sorted out behind the scenes.
New BP issued reflecting downgrade which allow OP and travel companion to claim compensation for the downgrade.
For sure I’m not saying that is what happened, as I say I wasn’t there, but I’d suggest we can not say any discrimination has occurred.