You are correct!
In that sense the asterisk wildcard is as greedy as e.g. in the Windows command prompt (Cmd) or the Search function in file Explorer. And (in my view) for clear reasons; see e.g. here
If it is important to have .tmp-files in subfolders of Subfolder included in your sync, you can define a second left-right pair one level deeper (at Subfolder level). Assume you have a present absolute path [Left1] and [Right1] to the left, respectively right-root folder of your sync.
The second left-right pair would then be [Left1]\Subfolder and [Right1]\Subfolder.
For this second left-right pair you can define a local Include filter
If Subfolder may contain a direct subfolder again named "Subfolder" (are you still there ...) you need to make your initial Exclude filter entry local to the first, initial left-right folder pair (otherwise your global Exclude filter would exclude any .tmp-files in the tree Subfolder\Subfolder)
Nevertheless, as I stated earlier in this forum, I would love to see RegEx support in Include/Exclude filter settings.
However, I know this is a lot to ask ...