Like I said, the Kaiser was a big talker.
Big talker or not, he was a credible threat. Imperial Germany was neck and neck with the USA as the most powerful industrial nation and had all its naval power concentrated in the North Sea with the potential to outbuild the Royal Navy over the coming decades.
It would have been irresponsible not to take that threat seriously and heavy as the casualties of WWI were, it was probably fought then and there rather than waiting for Germany to crush France and Russia and then watch on as Germany made itself even more powerful and Britain was forced to fight a war it couldn’t win against an ascendent Germany that was unrivaled and unchallenged anywhere in Europe.