It’s great that you found those instructions about how to use tar for this purpose, but please be aware that those are “generic” and don’t quite work in all cases in the DLS courses. Note that they omit the “h” argument on tar, so that linux “symlinks” are just included as links, which are not useful if they point outside the subtree that you are tarring up. Here’s a local thread on our Discourse forum that has more specific instructions.
The whole problem with the resnet50.h5 file is exactly that it is a symlink. So if you did the “tar” method following the generic instructions, the file is not really there. Please check it and then you may need to use the more specific procedure I linked above.