Optional dependencies, specified through the optdepends array in a PKGBUILD, can contain version restrictions like any dependency. Pacman ignores these completely, only caring for whether a package is installed or not, regardless of its version.

The attached PKGBUILD creates two packages, named "dependency" and "dependent". The latter optionally depends on dependency>2, which is not available as both have version 1-1.

Installing both, pacman notes:
(1/2) installing dependancy [########################################################################################] 100%
(2/2) installing dependent [########################################################################################] 100%
Optional dependencies for dependent
dependency>=2: for testing [installed]
which is wrong as dependency is not installed in a version greater or equal 2.

Querying the package database also erroneously reports this.
$ pacman -Qi dependent
[...]
Optional Deps : dependency>=2: for testing [installed]
[...]

Lastly, the warning when when removing dependency also reports so.
$ pacman -R dependent
checking dependencies...
:: dependent optionally requires dependency>=2: for testing
pacman -Rs dependent also does not suggest to remove dependancy.

The behavior on removal may be intentional, but the former two should clearly not denote that the dependency is [installed] as the required version is not provided.