When those interested in bitcoin as an idea differ on the direction of a project, they can choose from several options:
* Interpret the original texts in the way that they believe was intended
* Adapt the text or keep it fixed and rigid (like a Constitution)
* Adapt the text, change it and make it different
* Disregard it or propose something potentially better
The point here is that the above statement can be misunderstood very easily.
A constitution is not meant to be "carved in stone".
It sets out some general rules, "best practices", whatever you may call it, to govern the
process of
adapting a society's laws to meet the actual needs of their time.
Following that logic, you may easily call Satoshi's Whitepaper a "constitution" of some sort.
If, on the other hand, you were to conclude that nothing whatsoever may ever be changed at all, you're no longer talking about a constitution, but rather about scripture.
I guess what Bruce Fenton meant is an adaptable set of rules, but it's not really clear from his wording.
In which case I agree.