A 404 can be considered an error due to excess traffic, which a DDoS attack can cause. '404 not found' simply means that the data located on the server you are trying to accessed can't be accessed. Simple as that. It could be because the data is damaged, missing, or inaccessible at the current time.
Also, people need to learn the difference between 'DoS' and 'DDoS'. That bothers the shit out of me.