I really do not think it is because you downloaded the images differently. If you didn’t edit any other part of the code it should work. Have you tried restarting the whole notebook and running everything from the start?
I have been seeing this error also. I also used the bing dataloader and considered that it could be causing the issue, but I have reproduced this in a different notebook (and pip venv) loading the files directly from the directory and training a model.
I am using WSL and pip (with upstream pytorch installation instructions and pip install fastai)
EDIT: I wonder if some dependency snuck in a lock with an update? I could imagine environmental issue in my setup but if it shows up on collab that seems more like a bug?