Odd Departure in Appearance Scene

[lathspell]

Hey Dininziliel!

This is not the only time that Tolkien left us a mysterie. Another few are ofcourse the question: Did Hal see an Entwife in the North Moors? and many people once suspected Tolkien of being Iluvatar, though Tolkien denied this last one. I think that just as the two given above (and there will be more), this one also seems unexplainable with facts. But we can always speculate!

No, I don't think Tolkien wrote that part in an off-guard moment, for he himself said that every word in LotR was once, twice or thrice overthought. So that includes this bit when The Hunters see the old man. Tolkien put it there with a reason, but I do not know which one that is.

the horses would normally react calmly to Gandalf, not Saruman

I do not see why the horses would react differently by Gandalf or Saruman. None of them have an air of evilness, just as the Nazgul, to make the horses flee before them. Legolas mentions in the LotR - the White Rider - that: 'whether they fled at first in fear, or not, our horses met Shadowfax, their chieftain, and greeted him with joy.'
There is no evidence whatsoever that the horses were indeed scared away or that they just wondered off. The only thing Legolas hears the night they see the strange man is a happy whinnying and neighing.

The question who that man was I can not answer, but I do think that Tolkien wouldn't just put it in his books. Personally I think Tolkien didn't have any off-guard moments with his books, and if he had he would rewrite those parts.

greetings,
lathspell