28" = 700C?

from Gary’s Mt. Diablo invite:
>>I thought it would be fun to ride my 700c (28") unicycle

Wait a minute…I’m confused…does a 28" unicycle (like the Semcycle) use a
700c tire?

If the answer is no, then my second question is: is the Semcycle 28" tire the
only one available?

-Rick