I think BA's collective memory, always of fleeting duration, would have been steam rinsed by the pandemic, so I doubt that is a factor.

The usual reason for that reply is when someone didn't clearly and specifically claim EC261 Delay compensation. Or it was preemptive and they haven't seen the new message. I don't know if this was the case here but regardless, EC261 can't be avoided when claimed, so you can treat this as an early advance payment.