I read somwhere years ago that the stability equivalent between dihedral and wing sweep was such that it takes roughly 30 degrees of sweep to equal the effect of 5 degrees of dihedral.

The Toucan has a straight leading edge with a swept forward trailing edge. As such the sweep angle of the 25% chord line is very slight. Certainly not enough to be a factor based on that sweep to dihedral equivalency of 30 to 5. So it's no wonder that they would not have noticed anything.