The default is Scrolls => false. If the option Scrolls=>true is given, then a triple is returned, with the ideal first followed by xmat and ymat, the smaller and larger of the scrolls containing the carpet.
The source of this document is in /build/reproducible-path/macaulay2-1.25.05+ds/M2/Macaulay2/packages/K3Carpets.m2:1651:0.