I put the article through translate and it appears that this is the (translated) section you are talking about:
"To achieve this selection of 50 nuggets, the Tech Tour did not scan only the continent, but the whole world. The overall result for Europe is very encouraging since there are 284 companies (including 38 French) , compared to 121 in 2015. They are 181 in China, and 833 in the United States, a country where, nevertheless, injected are five times higher than those irrigating European nuggets."
The criteria for a "nugget" seems to be a company valued between
$100 mm and $1 B with annual growth > 50%.
The fact that the U.S. has more of these companies is not surprising. The US economy is equal to that in size of the EU but the tech sector in the US is much more robust. In the US there are 100,000 software and IT companies with less than 500 employees which would put them in this category. US tech makes up 25% of the global marketplace. The fact that there are more US companies that fall into this specific criteria is not surprising.
Whether or not this makes the US a better investment is a different question. The number of investable firms has nothing to do with return on investment. If all the European companies grew in value at an average of 10% and the US companies grew at an average of 5% then the European companies would be a better investment in terms of expected value. It may be that the European companies are much riskier and more likely to default which would offset that number. The number of companies that falls into this arbitrary and narrow criteria has nothing to do about the benefit of investing in either in Europe or the US.
Investment decisions are based on a multitude of factors. European regulatory risk, political stability, etc. may all be factors to consider when investing in a European company but it's difficult if not impossible to make a blanket statement about the quality of a country's investment opportunities.