This chapter—indeed, this Book III—reeks of distrust. For instance, Gandalf gets mistaken for Saruman (or his phantom) far too often—it had got me thinking that had Gandalf not announced himself in anyway before he entered Meduseld, Gríma’s reaction might have been, “What are you doing here, master?”
Then there’s this whole Lothlórien issue, which is part of the Rohirric culture, it seems. After all, Éorl was the first to show distrust:
[Éorl: ][N]one can pass, few or many, through the Dwimordene where dwells the White Lady and weaves nets that no mortal can pass.
UT III 2
Many others show it: Éomer, Háma, and of course, Gríma.
In midst of all this mistrust, Gandalf comes with these words:
[Gandalf: ][N]ow all friends should gather together, lest each singly be destroyed.
LR III 6
This, I think, is the lesson that every good citizen of Middle-earth needed to learn.
So sure, the Rohirrim may have initially distrusted the Huorns and the Ents, but by the time they rode to save Gondor (again), these Druedain-trusting chaps have gone a long way from the Dwimordene-fearing riders of Éorl.