Yes, that indicates that the pair is not properly coupled according to the applicable rules over the hatched length. For whatever reason differential pair routing rule violations can't be configured to produce the same kind of error markers and details as other kinds of violations AFAIK. They can be reported as part of a batch DRC, though, if you make sure to enable them in the "Rules To Check" section of the DRC options. Sometimes the error markers, including the hatch markers like this, get stuck, so you might need to use Tools > Reset Error Markers, and then re-run DRC to confirm if there's actually a violation there. The hatch indicators only seem to show up when you move one or the other of the tracks around, though, so clearing error markers and then nudging one of the tracks is another way to confirm what Altium thinks is going on.