Could be.
But i doubt that if so, it would have such nice, crisp, straight ends, at a 90 degree angle to the long side.
The foam used as dark slide slot seal in the magazine has different ends, and is also backed by a shiny, metal looking foil.
And when it comes out, it does so in crumbles.

So my guess is that it is not the foam from the magazine.

That is: the thing you have shown pictures of isn't.
It's quite possible, of course, that the seal in the magazine is coming out in bits as well.