There is no legal requirement for it to refer to MIL-SPEC. More often than not it is just pure marketing without any actual spec tied to it

Yeah if you see something labelling itself "MIL-SPEC", that's grade A snake oil bullshit.

That said military spec stuff is actually generally a good sign that something is of higher quality than random off the shelf garbage but only if you know there's a specific spec you want it to work with. And most of the time you aren't even necessarily looking for a MIL-STD (standard) but rather a MIL-PRF (performance rating/spec).

So like if something is "MIL-SPEC" run. But if you see say a spool of fiber that is "MIL-STD-1678 compliant" and more importantly "MIL-PRF-49291 compliant" and "MIL-PRF-85054 compliant", that's probably a really good sign that it'll do its job. The former PRF documenting perf requirements for the fiber itself and the latter PRF the cabling/sheath's corrosion and deterioration resistance.

It's the military so odds are it'll probably cost extra for that and it'll still kinda suck but it'll suck in exactly the way they promised.

Military grade afaict just implies the military ‘could’ use it, by that definition almost any company sells military grade products or services, except companies who explicitly would not sell to the military.