You should change the hillProportion value. At 70% water, you have 0.7 water, 0.2 land and 0.05 hill. You could try 0.15 land and 0.1 hill:
seaOption = {0.1,0.3,0.5,0.6,0.7,0.9},
landOption = {0.6,0.5,0.35,0.3,0.15,0.07},
hillOption = {0.25,0.15,0.1,0.05,0.1,0.02},
for example.
However, you may still not get enough hills because the heightmap may be too shallow.
If that's the case, you can try commenting the call to Blur() (self::Blur() in Create function), or increase the noise values, i.e. those:
collisionHeight = 40, -- height added when 2 plates collide
seaLevel = 0, -- base sea altitude
landLevel = 20, -- base land altitude
seaNoise = 6, -- max random sea altitude
landNoise = 9, -- max random land altitude
Just multiply everything by 10, the random should make some more noise that won't be blurred away.