The Huge Difference 

A blog, according to the dictionary is where an individual (or group) records information and opinions among other things, talking of one or several subjects. On the other hand, posts are entries found in a blog or social page that contain information and updates.

A blog consists of several posts which are sometimes related, posts include the date and the information the person would like to share. Blogs have a couple of "entries" which are found in "reverse chronological order", this means that the oldest posts are at the end and the recent ones are found in the beginning.
The article we read in class, explains how a blog that has only one entry (or post) isn't considered as one, because blogs contain several posts found in one common place (internet page).