if you train yourself by looking at GPL code then go implement your own things, is that code GPL?

it can be, depending on if it is different enough to convince a jury that it is not a copyright violation. See the lawsuits from Marvin Gaye's family to see how that can be unpredictable.

Of course not, because everyone making these arguments wants people to have some magic sauce so they get to ignore all the rules placed on the "artificial" thing.

If you copy and paste one line from a thousand different GPL projects, is the resulting program GPL?

Let's be honest about what's happening here.