The real meaning of the idiom "Nothing to shake a stick at" is that something is not very impressive. Here is a reference to its origins. Another, more understandable, version is "Nothing to write home about".
At first reading, I thought is was appropriate, after all 1GHz processor isn't much these days, but the exclamation mark indicates that he was impressed at the time of writing.
He has probably mixed up his idioms. The "not sure why" is just a remark about the absurdity of the idiom.