Crusty

Hello,

I've come across the following example for the word "Crusty" in the Oxford online dictionary under the definition "(Especially of an old person) easily irritated":

"Old crusty reporters know that when an official denies anything, it's a good time to begin probing it."

http://www.oxforddictionaries.com/definition/english/crusty?q=crusty

I was wondering if 'crusty' really serves to convey the sense of "easily irritated" here instead of something along the lines of "seasoned" and "experierenced." Mineral deposits or accumulations are often described as 'crusty' or as having a 'crusty' surface. Perhaps the word can be applied to people who have accumulated experience in a certain field of activity over a long time? None of the dictionaries I use cites such a figurative definition, however.

In the Merriam-Webster learners' dictionary, one of crusty's definitions is:
"harsh and unfriendly
? a crusty old man ? A crusty person often seems unfriendly at first but is really kinder and more caring than he or she seems. Crusty is usually used to describe old people."

http://www.learnersdictionary.com/definition/crusty

All the other dictionaries that I've checked define the word simply as unfriendly, easily irritated, surly etc,; none suggests that the word implies a redeeming quality of 'scratch beneath the surface and you will discover a nicer person.' Of course when you think of a crusty loaf of bread you can see the analogy: soft substance just underneath a hard but brittle shell. But I was wondering: to what extent when you hear someone being described as 'crusty' would you automatically assume that the person in question must be soft and nice at heart? To what extent is this connotation a part of the core definition of the word?

Thank you.