Interesting. The Biblical quote suggests that the watchmen were all looking in the same direction. The expression as used in idiom is - I am glad we see eye to eye on that subject - we both agree.
It doesn’t take much of a twist to change the original into the idiom. In other words by looking in the same direction as someone else, you share the same opinion. I don’t really know why the Oxford dictionary is sniffy about this by calling it a misquotation. After all, that’s language for you!