In the past weekly portion, Shelach, the names of the twelve scouts are mentioned by name + the names of their fathers.
Only Yehoshua is termed “bin Nun”.
Why the “chireq”?
In the sefer Sharei Aharon, he brings from the Ramban in Parshas Ki Tisa, that sometimes a chirik is used in place of a segel. The reason why it was chosen to use it here, and in fact he is usually called Yehoshua bin Nun, because it sounds like binun, from the word binah- understanding. This is to bring out the praise that there is no one that is a chacham v’navon (smart, understanding person) lie him.