There are definitions provided in the documentation as follows:
"Issues are entered by customers when they encounter questions or difficulties when following normal procedures. Records of issues are recorded, along with the steps taken to correct the issues. If you create a ticket as a copy of another ticket, the Status field displays all Status values."
Issue Management - CA Service Management - 14.1 - CA Technologies Documentation
"Incidents are events outside of normal operations. When an incident occurs, it disrupts the normal operational processes of an organization."
Incident Management - CA Service Management - 14.1 - CA Technologies Documentation
From a technical perspective while Incidents/Problems/Requests have a lot of overlap (as they share the same tables) Issues are completely separate.
Also if I'm not mistaken Issues don't really fit the ITIL standards, but are present to provide a means of tracking things that don't necessarily fit into the regular ticket types.