I know very well what is said, I actually quoted the exact statement earlier, in case you didn't notice.

Now, it does say that it "seals her powers", but something must be sending those signals, and judging by the content of the messages, it must certainly be coming from Adels seal, do you agree? After all, the static is a result of Adels seal jamming radio waves, so any hidden messages found in the static would almost certainly have to come from the seal, as no one in Galbadia has any control over the static.

Then, we analyse the content of the messages:

1. "I'm alive" (Adel was only frozen down, not killed).
2. "Bring me back there (Adel wants to be freed and return to earth for obvious reasons).
3. "I'll never let you forget me" (Adel would be bitter at losing her dominance over the FF8 world, and wouldn't forget about it so easily).

So, we have interference coming from Adels seal, containing messages sounding exactly like something Adel would say. What is the logical conclusion to draw then, considering that there are no other explanations given? Certainly, that Adel still has a tiny bit of power; just enough willpower to let those those three small thoughts seep out into the jammed radio-waves, despite the powerful seal.

Of course, if you can come up with an alternate, plausible explanation for who or what might be sending the messages, then by all means, go ahead. But if not, we must conclude that it is Adel.