You're correct.
And now I've cleaned it and got the frame into some decent light, I can see all the other brush touch-ups done in the past. The main colour is definitely not metallic or glittery and definitely a non metal grey.
I'm not planning on restoring the bike...it's quite clean and crack/corrosion-free. I just want to get it roadworthy and reliable. Besides, the area I need to touch up is completely out of view, so it's not desperate.
It wouldn't hurt, I suppose, to sand back a small area to see if there is any useful paint history to go on
Thanks