Naturally, there is a lot more to the story on the junkyard metals sorting. That chart is merely a suggested starting point, IMO. Over the years, steel makers are constantly changing things, and what may have been in common use 20 years ago has been replaced with something superior. So take it with a grain of salt....or maybe a lb. Add to that all the possibilities of heat treatment. If you find a finished part, yes, chances are pretty good that it has been heat treated. To what though? You can get such a variety of properties from so many alloys that even if your guess is correct on the metal type, you odds on guessing the HT condition aren't as good. About all you can do is take a file with you and check for hardness. Or if you wanted a correct set of hardness testing files.
The chart is not without merit, but there are caveats. Lots of good stuff can be found at the scrap yard. Ideally, since many metals are marked from the factory or distributor, you can find a piece large enough to still have some markings to ID it. But I wouldn't count on it. Around here, the local scrapers don't allow us to scrounge anymore anyway, so it doesn't help us. They used to, and I have a sneaking feeling that some of their regular customers might still get the privilege, but not most of us. There is a place in Jacksonville, a little town about 45 mins south of me that advertises sales of metals of all types. I've not visited with them, but I have often wondered if they are a distributor in disguise for a few larger companies.