Looks to me like a case of poor quality steel. I doubt the pinching at the back would have happened on a good post. I've never seen that and I've owned some funky bikes over the years.
Now that bend looks just like the bend my Hupel Rider post took (except yours is bent considerably more) when I hit a frost heave going >50 mph (80 kph) racing a mountain descent. Hupel Rider - a cheap post of soft aluminum. Replaced it with a Zeus post of much higher quality and had no more issue.
There are lots of steel posts like yours that are strong enough to have as much showing as yours and suffer all kinds of abuse. I've never heard of a Raleigh 3-speed post bending and some of those have seen epic abuse. If they bent, my dad would have passed on that story to me. He an d his buddies were some of those abusers. Measure up the diameter of your post and look for a new one.
Ben