You’re quite welcome!
convert_to_inference_data is a pretty feature-sparse conversion of a data type to an InferenceData. In this case, it takes the data in stan_chns and converts it. Stan’s output doesn’t differentiate between generated quantities and parameters and moreover between log likelihood and posterior predictions. If you want generated quantities to be treated specially in ArviZ, you’ll want to use a specialized conversion function.
In ArviZ, these start with from_. from_mcmcchains or from_cmdstan will work for you. Check out the worked example using CmdStan on 8 schools in the quickstart for the signature.