Can one see flickering of a light bulb at 50 Hz?
Short answer
Yes, the flickering of a light bulb may be noticeable, and yes, that's directly related to the mains frequency. However, since the flickering of a bulb is about two times higher than the temporal limits of our visual system, it is unlikely to be perceivable.   

Background
The temporal resolution of the visual system can be quantified in a number of ways. As you are referring to a relatively simple flickering stimulus, the critical flicker fusion frequency is probably the most relevant. At a certain critical frequency, a flickering stimulus will appear as a continuous stimulus. This critical flicker fusion frequency limit is around 50 Hz, but variable between 5 - 50 Hz, dependent on the lighting conditions (Kalloniatis &amp; Luu), see Fig. 1 below.

For example, the turn signal of a car is obviously flickering (flickering in the 1 Hz region). But an object displayed on a standard flat-screen computer seems steady. A monitor's refresh rate is typically 60 Hz, which is indeed above the critical flicker fusion frequency (Holcomb, 2009). 

However, the good old CRT screens can sometimes seem to be flickering. The mains, as you indicate, is indeed 50 Hz (Europe, Australia) or 60 Hz (US), and indeed the flickering is at this frequency. Similarly, well functioning fluorescent tubes seem to flicker on occasion (when they are reaching their end they start to flicker too, but that's because of a failure of the device rather than the mains frequency peaking through). Due to a similar effect, light bulbs may seem to flicker too. However, because of the sine wave characteristic of the mains alternative current, featuring two peaks per wavelength (a negative and positive peak, the flickering of a light bulb is actually two times the mains frequency, or 100 - 120 Hz. This is quite far above the critical flicker fusion limit and hence will likely not be noticeable.

It's interesting to see that you mention that it was around sunset. Scotopic vision (night vision) is mediated mainly by the rod photoreceptors. The rod visual system mediates gray scale vision at low-lighting. While spatial resolution is poor, it's very well adapted to process fast-moving stimuli. Hence, the flicker fusion frequency under scotopic viewing conditions may indeed be higher; i.e., flickering of light bulbs may not be perceived during the day (Federov &amp; Mkrticheva, 1938). Nice add-on there.   

To add to this as alluded to in the comments, whether the flicker of mains-grid powered appliances are actually visible depends on a lot of factors other than flicker frequency. CRT screens, for instance, may have improved phosphors that have delayed response times, 'smearing' out the flickering into invisibility. In other words, it's not a simple matter of 'ON' and 'OFF'. Likewise, light bulbs heat up and hence the temperature difference might not be noticeable to us, as the temporal flickering depends on heating and cooling of the wire.     


Fig. 1. Flicker fusion as a function of stimulus intensity. Note that the shape of this graph means that photopic vision is less sensitive to temporal changes; the intensity scale relates to the stimulus intensity, as alluded to in the other answer. Scotopic vision to promote the temporal resolution of vision in the sense mentioned in this answer alludes to the ambient lighting conditions conditions. source: Kalloniatis &amp; Luu (2007) 

References
- Federov &amp; Mkrticheva, Nature; 142: 750–1
- Holcomb, Trends Cog Sci 2009; 13(5): 216-21
- Kalloniatis &amp; Luu, WebVision, chapter "Temporal Resolution" 2007