Unfortunately, there is no easy way to determine the DML command used without having some kind of auditing setup prior to the action.
You might be able to infer whether the action was a
DELETE or a
TRUNCATE by looking at the transaction log to see if pages were deallocated or if row data was written to the log. If the trnasaction log shows pages were deallocated you can be certain that the table was truncated.
If you had SQL Server trace or an Extended Events session running on the server at the time the delete occurred, and that trace/session is capturing DML statements, you'd be able to see exactly what happened.
Probably the more important consideration would be to ensure you have a Recovery Point Objective that serves the business by limiting the amount of time that can go by without a backup happening that you can use for recovery. So, with full recovery, you could be running log backups every 5 minutes, which would mean you could recover the table to a point just before the delete took place.