Some of the samples accounted for the in the "Other" category were probably sampled from system modules, i.e. anything under the Windows system folder.
To include the details of system modules in the display, click the "System Modules Hidden" link above the 5 Hottest Functions table, and use the Display Filter dialog to enable the display of system modules.
To get a complete detailed breakdown of the distribution of samples among functions click the "Functions" node in the explorer tree on the left.
Hope this helps,