To be fair, that circuit uses a LPF with a more sensible L to C ratio for a 50Ω design so the LPF will appear fairly transparent up to the cutoff frequency. It looks like a regular 50Ω LPF design. I don't really have an issue with that LPF as it probably won't have much (if any) impact on the input impedance of the probe.
By contrast, the LPF in the thesis has tweaked component values and this will cause the issues I described in my earlier post because it isn't a 50Ω filter anymore.