I have quoted that story for years until I started to find WW2 ordnance tables that show it was 99.9% impossible. I recently found this site that includes a page from a British penetration chart showing the 37mm APC M51 chance of poking holes in Tiger Is and Panthers at 0, 30 and 60 angle-off.
Considering the penchant for US troops to consider every panzer a Tiger, I can believe they killed a Panzer IV. I still like the David v Goliath story, though.