I guess the guy who wrote the article was trying to say that the main reasons for having trouble are:
1. Don't know what you're doing (Theory)
2. Can't hear it in your head (Aural) and
3. Can't play it anyway (Technique)
Which is pretty hard to disagree with.
But I think he left out another important one:
4. Ain't got nothing to say....
Despite all his stuff about how creative humans are, the truth is that many actually aren't very creative. It's no big deal. Some people are very creative in some areas and not in others. Others are fine copiers but feel uncomfortable when given a 'blank sheet'.
There are many fine professional musicians who never wrote a half decent song and who almost exclusively play work written by other people. Perhaps their creativity lies in the expressiveness they can bring to their playing, or in other areas. At the other end of the scale are enthusiasts who never manage to learn somebody else's song properly all the way through and do nothing but muck around in an 'original' but fairly ineffective way.
...cough... I don't know anybody like the last example myself of course...
I reckon that once you've got something different to say, most players will figure out a way to put it into music. Until then, some people never really take to improvising, whereas others have trouble stopping themselves improvising and struggle to play in a more disciplined 'as written' way. I think it's good to keep trying to extend your weaker areas, but not to get too bothered if your main strengths turn out to lie elsewhere. Just as long as you keep playing...
Cheers,
Chris