This depends on the teen. In my peer group, at the time, a few of us being nudged by a mentor or two, went right after the machine code.
One of the things that mentor emphasized was writing a dissassembler soon after becoming familiar with a given CPU.
However, that woild be post fact. Some teens got closed computers, like Atari machines. By todays standards, they are wide open. Back then, they were mysterious, but capable with spiffy graphics and sound chips. The key thing was how users were nudged toward or away from the guts of it all.
Other teens got, say an Apple 2. On that one, you got schematics, a commented ROM listing, and the whole machine was open, software driven. It screamed, "hack me!" The whole damn computer was a clever hack!
Again, my per group were Apple people, and were writing ML based off the snippets found in the ROM, along with great tutorials found in the grocery store magazines. (Where I got my first dissassembler, BTW. Thank you COMPUTE!)
This stuff varied extremely widely. One town would have that spark of learning, a particular school, or club maybe. Another one, nothing. Just gaming, the usual.
Circling back, yeah. Those DATA statements were known to be programs. Lots of us hand disassembled them and either wrote them down (I have a couple in some papers somewhere, I am sure), and my preference was to add REM statements with assembly code in them for later. Oh how I would have loved BBC Basic!
The Apple was cool, had a monitor and mini assembler, disassembler. Wrote a lot with it. Still a mess compared to what I understand the BBC had. I want to go and run one.
Other machines varied, as did people and what books and or other resources were available to them.