By definition a linar ring is closed so always return true. This is checked in the constructor.
[Visual Basic]
Overrides Public Function IsClosed() As Boolean Implements _
ICurve.IsClosed
True if the linear ring is closed.
Missing <remarks> documentation for M:Geotools.Geometries.LinearRing.IsClosed
LinearRing Class | LinearRing Members | Geotools.Geometries Namespace