What is the impedance value that means it is a low ESR capacitor?
In general, the impedance of a capacitor with an ESR can be computed as \begin{equation} \dot{Z}_c = ESR - i\frac{1}{\omega C}.\end{equation} Then, knowing the frequency at which the total impedance is given (f = 100 kHz), just solve the equation for ESR. 

Usually, values of ESR higher than 0.1 ohm are considered to be "high", but of course that greatly depends on your application.