EZ Inventory only keeps track of changes made by the app itself, it won't be able to keep track of inventory changes that occurred outside the app.

For a more complete view of inventory changes for each variant, this is possible to see via the Shopify Admin.  The Shopify Admin provides a history of changes that occurred in the last 90 days and who/what made the changes.

To do so, go to the variant detail page in the Shopify Admin, then under the "Inventory" section, click the link "Adjustment history" as shown below:

On the next page, it will give you the date and time when the change occurred and also the name of the staff or the app that made the adjustment:

One thing to note here is the Shopify Admin will only record changes to the inventory quantity.  So if you use EZ Inventory to update the quantity every hour automatically, for example, and there were no changes to the quantity since the previous run, then you won't see an entry for it in the Shopify Admin.