Why is there a difference in the ticket count between a ticket export and the reports?

The ticket export takes into account the merged tickets which are not included in the count for the reports. 

For example, if three tickets are merged together, the reports will see that as one ticket; whereas the ticket export would see them as separate tickets. This is one of the reasons for a discrepancy in ticket count. 

Merged tickets would not be taken into consideration while generating reports in Analytics

Please refer to How do I export my tickets from Freshdesk to export tickets from List view.