I have kinked a few bikes...the cause is a frontal impact. The top tube probably shows some subtle deformation as well. If the fork is stronger than the frame the frame is kinked in this fashion. Nothing is compromised, really, if no cracks are present. The handling is different than it was before the frame was tweaked, but if the head on was head on, the symmetry of the frame may not even be compromised.

If you've owned it for 40 years...what the heck is it? We need some more pictures...of course. Easthill, you're welcome.