I don’t Know if I understand ur question but if u mean distinguishing the class of an implemented model architecture from one that is not a model then the only difference is that model classes in pytorch inherit from torch.nn.Module.
If u are referring to ones that make up a NN model architecture like torch.nn.Linear, torch.nn.Conv2D etc and are trying to differentiate them from things like loss functions eg: torch.nn.CrossEntropy or torch.nn.NLLLoss etc then I guess u just different them by there names, by the names u know which can constitute a model architecture and which is a loss function