Ok. Let’s assume you’re right. It is not a Muslim prayer rug. Doesn’t change anything for me. A rug with Arabic writing on it is found on the border. That tells me all I need to know. What the rug was used for is irrelevant.
I always wonder about these stories about finding Iranian money, too. Why on earth would terrorist infiltrators be carrying Iranian money?
The mihrab, which probably derives from the prayer niche in mosques,
must point toward Mecca while the rug is in use.
So any rug with a Mihrab or point can be used. From the photo we cannot determine
if such a design is on the rug. It's possible that the guards opened it up and saw it.
I would think that they know what the interpretation of such a design would be which
is why it's being called a Muslim prayer rug.