I agree, I also think there is some weirdness going on with the 'we can presume it has infinite memory'. There seems to be many assumptions of different strength all waved with that same phrase, depending on the system in question.
Edit: ok I get it. Still, GP observation is hardly at that level from my (limited) perspective. Not being able to advance by itself means it's not a standalone system - otoh external actor is obviously implicit for many other examples as well. I suppose they (and me) are taking the word machine too literally.
But "pens are Turing-complete" seems a bit, well, diluted.