What does 50%TTL - 10/90% RF mean for a switching speed measurement?
We know there are many conversion factors from rise time and frequency response or delay time depending on the differences in performance critieria.  $$\omega=1/RC$$ where the time of this voltage rise time= 1-(1/e) = 63.2% of V+ at t = RC.

But here the criteria is different.

For logic the critical factor is latency to reach switching threshold, which for TTL is actually 1.35V~1.4V or two Vbe drops, although 74HCT=1.5V approx.  and  NOT Vcc/2,  for CMOS logic emulating TTL thresholds, but traditional CMOS logic is Vcc/2 with symmettric impedance and symmettric Vgs(th) Pch and Nch devices with a tolerance of 25% over temp .  

So we can say Vdd/2 or Vcc/2 or 50%TTL, to mean CMOS logic but with the understanding that 74HC is different than 74HCT . The mean threshold is often never specified but is acutally the mean or average  level of Vih and Vil for any given Vdd and say 10% tolerance on Vdd. So often specified at 4.5V for 5V logic, etc.

The true threhold and this range is reserved for noise and thermal shift so that statistically you have a saturated logic level that had the potential for an extremely high SNR and hence extremely low bit error rate.  

For RF the critical measurement is the bandwidth of the power slew rate of voltage and for simple filters this can be proven to be 10~90% rise/fall time of full scale $$f_{-3dB ~BW} = 0.35 / t_r(\text{10~90%}) $$

These 1P3T Pin diode switches are designed for both RF,  Logic and other similar switched power circuits, they specify two conditions for simplification and the implication is delay time or maximum frequency bandwidth in each case for maximum toggle rate. The caps are small with low ESR, low ESL (nH) or high SRF (MHz).

There are other factors, but this is the basic interpretation.  The 1N4148 bypass caps are intended to speed up the switching time of the input steering diode to drive the pin diode at minimum reponse time with a parallel shunt R to discharge the cap between switching cycles.