Unfortunately, there's almost zero documentation for any of these crates.
That's sadly true. But, if you click the src button near the function, you can see these functions are just wrappers over GDK-PixBuf C API, which is documented. Check out:
Looks like all these three methods expect different file formats – from_bytes expect to read raw array of values, from_inline expects some internal GDK-resource format, so only from_file is able to understand usual image formats like png or jpg.
If you want to avoid the need to create a temporary file, by best guess would be to try one of the from_stream functions, as gdk_pixbuf_new_from_stream also documents that The file format is detected automatically.