Yes square as in straight edges and no I am not lying here.
The most difficult part of this technique is to tat with an additional core thread.
If the pattern stats: R 5-5-5-5, Ch 5-5. You will simply not tat over the second core thread by the double stitch before and after the picots (A).
You will see the extra core thread at the picots (B). By pulling on the additional core thread you will see the ring becomes squarer like and there the additional thread was, is now corners (C).