Slizzer,
its a combination of two factors:
1. As the coach noted, extensive active stretching needs to be done along with extreme strength work or else, you will get less and less flexible. This adaptation to high level strength work is simple - the body wants to become more efficient in what it does.
For example, one of my problems to achieve a fully open shoulder angle was my constant practice of one arm chin ups. I feel in order to maintain this ability my shoulder joint 'wants' to remain tight and rigid -then it is much more efficient in chinning. My observation of climbers and aerialists further proves this point - they always have tight shoulders and problems in their handstand work. (which they do occasionaly, as all circus people do)
Having said that, it does not mean one cannot achieve both to a large extent, but serious time and work needs to be invested in active stretching if one wants to maintain or improve this aspect along with high end strength training.
2. From asthetic perspective a muscular guy will always have a problem. Whether it is capoeira, wushu, dance or free form movement it looks more articulated, free, flowing and expressive with long limbed, less muscular people. I need to make an extra effort to fully articulate motions and perform them in a larger ROM in order to remain expressive to the same degree as those lanky individuals. My girlfriend for example, (a professional dancer) is my exact opposite. She is taller than me, thin and long. Now the good side of the coin is that I have and always had a very easy time with strength, balance, agility.
I have tried for periods of time to become this thin-longer guy. I stopped strength training and tried to do everything I feel is right and essential to a human, even long distance running (!). It resulted in depression and injuries. I realized, this is not in my nature.
Ido.