It still showed the “oh wow” paragraph because the browser is programmed to “move” the closing </body> (and </html>) tag(s) placed by the coder, in case there’s more content under these tags, and will place it (or them) at the very end of the code (and so what you wrote after the </body> tag now ended up as a child of <body> and therefore it’s displayed if it’s an element that is supposed to be displayed).
Some browsers might not do this and thus some problems might arise, so it’s best to not have anything after the closing </body> tag (except the closing </html> tag in case you opened it).