Why is the output inverted for this SPICE model
In LTspice, exponentiation is **, not ^ (which is meant as XOR). Just search and replace the two occurences of it. Instead of:

+ {70m*REL_CTR*(8.448148613*0.998979389^(1/(abs(I(Vsense))+0.1p))*
+ I(Vsense)^0.449371295)/18k} (0,0) (0.3m,0.3m)

have:

+ {70m*REL_CTR*(8.448148613*0.998979389**(1/(abs(I(Vsense))+0.1p))*
+ I(Vsense)**0.449371295)/18k} (0,0) (0.3m,0.3m)