Was kicking out some KRFC founders an example of "founder's syndrome" -- a natural phase of a maturing organization?

No, even though it may look that way because founders were involved in
a disagreement.

Founder's syndrome occurs when an organization's founders are still
in positions of leadership or management, and resist accepting and
leading the changes necessary for the organization to mature, such as
formal financial accounting, clear (and therefore less flexible and
fun) roles and responsibilities, or sharing power and responsibility
(reducing their control, but also enabling all of the now-increased work
to get done).

The people whose memberships were revoked were not in formal leadership
positions so don't qualify for the syndrome. Each of them also helped
create and participate in systems necessary for organizational maturity.

Conflict at KRFC may be more closely related to community researcher
Diana Leaf Christian's "structural conflict" than founder's syndrome:

problems that occurred because founders didn't explicitly put certain
processes in place or make certain important decisions at the
beginning, creating one or more omissions in their organizational
structure. Several weeks, months, or even years later the group
would erupt in major conflict that could have been largely prevented
if they had handled these issues early on. Naturally, this sets
off a great deal of interpersonal conflict too, making the initial
"structural" conflict even worse.