Yes unfortunately "model craft" is not defined anywhere in Part 97 that I can find.

I can't say I understand the rest of the first paragraph - Part 97 doesn't actually ban encryption, just "codes or ciphers intended to obscure the meaning of the communication", from which "telecommand of model craft" is specifically exempted.

I'm not as familiar with the Part 15 rules - do they allow high gain antennas? Since this case is about stationary command and control, I wonder if lower power + high gain wifi antennas at both ends would close the link.