Aren’t we talking about enforcing/exercising a legal right?

Whether you have a reason to make a claim is much different than whether you have a legal basis for your claim.

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.

EDIT: Although that seems like largely just a semantics thing. Like if a judge orders a company to pay you some money and you say "give it to austhrow743" is it valid to say that I have a right to that money? Or is it that you have the right that I get that money? If someone wants to phrase "linux kernel copyright holders have a right to demand users of their code share it with anyone who asks" as "anyone who asks has a right to that code" then I don't really have a problem with that.

I just see a big difference between making a request and making a claim. I don't need to think I'm legally entitled to something to ask for it. I don't even need to think that getting it is likely. Whereas Abigail appears to be treating sending and receiving requests by emails as equivalent to a court summons.