The Pythagorean theorem for example can be traced back, in an incomplete form, all the way to Ancient Babylon (older than 1500 BCE), and there were also Indian texts mentioning the theorem around 800-400 BCE. The thing is, a lot of mathematics was already being done before the famous Greeks that we associate them with wrote them down the way that they did. Over time though, a Eurocentric view on science (and history in general) would form, and the knowledge built up by other civilizations became less well known for its origins as it was absorbed into European knowledge.

During the European Middle Ages, the Greek legacy of mathematics mostly only survived in the East while Europe went through its so-called Dark Age. One of the main reasons we even still have these ancient Greek texts, is because they were still being copied and used in the Arab world at this time, which led to science flourishing in the Islam world. Most well-known is probably al-Khwarizmi, who is credited with having invented algebra, but plenty of other Arab scholars were making advances during this period in a number of fields ranging from mathematics to historiography.

Meanwhile, European science had somewhat halted to a grind. The church as an institution had become pretty much the only source of scholarly research, but everything had to fit into a rigid worldview, partly based on Aristoteles and Plato, and partly based on the Christian doctrine of a perfect creator. This roughly lasted until the Renaissance, when the rediscovery of old European texts, combined with intensified contacts with the rest of the world meant a new boom in science and a step away from the Christian doctrine. This would eventually culminate in the Enlightenment with the advent of the modern scientific method.

But throughout the Middle Ages, before European scientists had started using the scientific method to make large strides in our understanding of the world, other cultures certainly weren't completely backward scientifically. In fact, recent research has focused on the way Europeans managed to catalogue all the knowledge that had been gathered before them as they spread out into the world after the 1500s, and use it to their own advantage. When sailors and traders arrived in (South-)Eastern Asia for example, there was a strong incentive to find out what indigenous plants were available, and which ones could be sold for a good profit. To this end, scientists working for the VOC set about making a botanical overview of the local plants, and in this monumental effort were aided by local botanists who already had a massive knowledge of the local flora.

The same thing happened with a lot of other fields of research, and in a sense this would help spur the encyclopedic age, exemplified by Diderot's Encyclopedie. As Europeans gained more access to the knowledge of a varied amounts of cultures, they catalogued all they could, and would take the useful bits for their own use. I've already mentioned al-Khwarizmi, his works and others from the Golden Age of Islam were widely translated and read in Europe, and their concepts of mathematics were essential in developing Western mathematics as we know it today. There are scholars who claim that Descartes for example was strongly influenced by al-Ghazali, an Arab thinker, when he conceived of his famous "I think therefore I am."

So to recap, yes, there is a strong Eurocentric bias in the history of science. In truth, all science is a collaborative effort. Just as Arab thinkers built on both the Greeks and Indians when they made great strides in science and mathematics, so too did the Europeans build upon the foundations that had been laid out for them by those who came before.