We're talking about Lost-Entrepreneur439 on Reddit emailing a company to ask for some of their code.
You can just do that. No GPL, open source, enforcement, demands, etc language needed. Just "I'm trying to do X, can I see the code for Y?". I receive and send them at work pretty frequently.
They've mentioned the GPL as a way to try to increase the chances of getting sent the code. A support person for a medical device company might not know anything about software licences or linux or GPL. If the company has some sort of "send GPL code to askers" policy and Lost-Entrepreneur439 just asks for the linux kernel, the support person might not know that the GPL policy applies and just say no. If you include it in your message then it increases the chances of them typing "GPL" in to whatever internal knowledge bank they have and seeing "for GPL requests, forward the enquiry to jeff@ourcompany.com" or something like that.
The GPL isn't between Lost-Entrepreneur439 and the company so I don't think "enforcement/exercising a legal right" is an accurate way to describe what we're talking about. That would be if the copyright holders to the linux kernel get involved.