The problem is; we're so used to the African sun - so to us, 25c is just an average day. 30c is a little warm.
The UK has below 20c temps for most of the year and down to past -0c - which we do not have very often.
So, whilst you may mock; it's all relative. To them, they are having a heatwave and it is very hot for them. They're not used to such temps and neither are homes built of such temps.
When my wife moved out to SA - she would have her bathing suit out, in the middle of winter at 15c because "its hot" whilst I would be freezing my nips off.
Today, anything below 20c is cold to her - because she has adapted.
People in Nevada will laugh at us when we're saying 37c is too hot and a heatwave, When to them, it's just a normal day in July.
So, to me it seems silly to mock the British for moaning about the heatwave.