Read this, real named persons with their quotes, and references FROM THAT ERA it is not a legend it is history.
https://supplystudies.com/2017/07/26/the-making-of-made-in/
I have read it and it is very interesting and enlightning. I still don't see that the Act was
aimed at Germany. It seems it affected Germany most because they were the largest trader or supplier.
German manufacturers did not sell directly to the British public but to importers/merchants who were the ones trying to pass inferior imported goods as "made in England". The Act was directly aimed against such practices and against the English merchants who engaged in them and it only affected German merchants indirectly.
A German merchant was not obligated to mark his goods for export as "Made in Germany" but the importing merchant was obligated to not misrepresent their origin. He did not even have to say where they were made but he could not say they were "Made in England" when in fact they were not.
Again, reading the act, I see a clear intention of regulating the market with "truth in advertising" and not any intention to single out any country in particular.
It was trying to avoid misrepresentation of the origin of goods and even gives the example that garments made in England should not be made to appear as if made in France, which, I assume, was more desirable.
I guess if you look at it from a certain point you could make the case that it affected Germany most.
And, let us not forget that Germany in the late 19th century was quite a powerhouse. Their steel, chemical and other industries were first rate and in the late 19th century and first half of the 20th century they managed to use all that to give the world quite some headaches for which the world needed quite some aspirin.