What does a humbling experience mean?
Solution 1:
Yes, indeed, it can and does mean "something that makes him feel insignificant or inferior" in this situation. Although he was being knighted, and therefore singled out as significant and elevated in status, that does not mean the experience made him feel that way. He probably felt, even as a Knight, that he was insignificant and inferior compared to the other people at the ceremony, such as the other people being knighted, and of course Prince Charles.