In order to access any of the data in the Backup section such as text messages, notes, and voicemail, you must choose Load Backup Data or Back Up Now which will make an iTunes backup. The reason you need to make an iTunes backup first is due to the fact that text messages and the other data in the Backup section is all stored closer to the root of iOS which is impossible to get to without Jailbreaking (hacking) iOS. The only way iExplorer gains access to that data on a non-Jailbroken device is because iTunes backs it up.
All other sections of iExplorer such as Media, Apps, Photos, Media Library, Books, and Root (with Jailbreak) are a direct connection to your device and read the data directly from it without requiring an iTunes Backup.
Then, just so you know, an iOS device can backup in iTunes on any computer without performing a sync and making that its primary computer. Just cancel any prompts to sync in iTunes and to prevent them, you can go into iTunes Preferences, and on the Devices tab, check the box to “Prevent iPods, iPhones, and iPads from syncing automatically”. Checking that box will prevent any auto-syncs and will help avoid dataloss due to iTunes syncing when you don’t want it to.
Once you are done exporting your data, you could then delete the iTunes backup in iTunes Preferences on the Devices tab. You’ll see a list of backups on that tab with the name of the device and the date/time of backup. Just highlight one and click on Delete Backup. Once a backup is deleted in iTunes Preferences, then just quit and reopen iExplorer to have it also cleared from it.