First step with a production bike is to investigate your warranty options.
Assuming that's not an option, is it just a pin hole or is there a crack propagating from the hole? If it's just a hole, that's definitely a weld defect but might not ever cause a problem. It's been there since it was new, so the fact that the frame is 7 years old and it hasn't started to crack gives more reason to just keep an eye on it. Holes like that in the middle of a weld don't ever appear once the weld has solidified. They either pop up when the weld is still molten or not at all. If there is a crack along with the hole, 70s-X is a good choice. I'm not sold on the idea of adding extra material as I don't think it's a design flaw, just poor execution.