I'd have done the same Paul.
From a practical point of view, there is always a remote chance that the waiting time could have allowed the stain to become more difficult to remove. And hey, accidents happen.
You then have the possibility that this engineer may remember you and something positive could come out in the future.
Of course, there are those who would become angry and demonstrative saying it's their problem, let them sort it out or I'll sue, but hey, I've got better things to do in life

Have you ever scuffed any paint whilst on site yourself? Chances are if you tell the customer, they'll say don't worry, we've got some paint left, I'll just touch it up. Same sort of thing.
Safe and happy cleaning

The Ken