When learning or brushing up on a skill, it helps to use an existing work as a jumping board. Painters do this by producing copies of the old masters, and FFC could be construed as the programming equivalent.

While a company can copyright artwork (and music), a game mechanic cannot be patented (no matter how hard Wizards of the Coast may try). Even if Square hands down a C&D, Gleeok can simply strip out the copywritten components and the grounds for lawsuit would evaporate. In a way FFC has an even easier means of doing this due to the way it is being programmed (and would be even easier if it had a different name, like Catastrophe).