Meteorological meanings

I'm confused about the long-term weather forecast from the Weather Network. I understand that we might be seeing storms on Friday and on Saturday. But what struck me as odd was the distinction between a thunderstorm and a thunder-shower (and the necessity for a hyphen in one but not the other). It seems that the former is used for a more severe storm, although the US National Weather Service explains (slightly disdainfully, I think) that technically there is no difference and that:

In fact, in order to avoid confusion, we in the National Weather Service do not use the term "thundershower". If a shower is strong enough to produce lightning, even just one single bolt, it's called a thunderstorm.

The difference between a risk and a chance of seeing one or the other is more puzzling. You might think that a 60% probability of precipitation (P.O.P.) compared to 40% might explain the difference in terminology, but apparently not, as today's forecast talks about chance at both percentages:


So I think it must come down to a difference in perceived levels of danger - thunderstorms being something inherently risky, while thundershowers are less so? Maybe I'm spending far too much time worrying about this...