In programming, "source" and "asset" have specific meanings that conflict with how you used them.
Source is the input to some built artifact. It is the source of that artifact. As in: where the artifact comes from. Textual input is absolutely the source of the ML model. What you are using "source" as is analogous to the source of the compiler in traditional programming.
Asset is an artifact used as input, that is revered verbatim by the output. For example, a logo baked into an application to be rendered in the UI. The compilation of the program doesn't make a new logo, it just moves the asset into the built artifact.