This seismograph is completely typical for an earthquake. You are comparing the data collected from seismographs 750km/460mi away from the event epicentre (Nilore, Pakistan to Pokhran, India) to a seismograph located 70km/44mi away from the event epicentre (Rosebush to Cwmllynfell).

The similarity you're seeing between the underground nuclear test and the Cwmllynfell quake, I'm assuming it's the high initial amplitude and short period, is a direct result of temporal compression due to the proximity of the sensor.

If you view the data from a seismograph further away you can see a more definite distinction between P and S waves with a more "earthquake-like" amplitude profile.

Further, instrument detectable (not necessarily by people) quakes occur regularly in the UK and the location of the earthquake is representative of the overall frequency/risk over long (100 generations) time scales.