Going back to the philosophical debates of the ancient Greeks two of the most prominent competing overarching theories of the nature of the Universe in general were teleology vs. mechanism. Teleological beliefs are those that say that things exist or happen for a reason. For example, the idea that the reason clouds exist is to provide rain to water crops so that humans can grow food for themselves. It elevates "purpose" and indeed the concept of sentience or conscious thought to the level of fundamental force in the Universe. Competing against that is the theory that the underlying structure of the Universe is fundamentally mechanistic, based on simple rules and brainless processes without underlying final purpose. Things such as conscious thought and human life aren't planned for integral aspects to the Universe, rather they are emergent accidental phenomena. The process of science has over time settled on a decidedly mechanistic view of the Universe.

In other words, your professor is warning you against the idea that things happen in history purposefully to enable other things in the future that result. For example, it has been very common to elevate the early democracies in Greece by seeing them as intentional ancestors of modern westernized democracies. To see Charlemagne as the creator of France. Or view WWI through the lens of WWII. Especially since so much of history comes down to the actions of individuals acting on their own motivations it's very easy to cast new motivations on them based on what was happening elsewhere or what would happen later. A lot of history comes down to things happening by accident combined with very complex motivations by numerous individuals some of whom are acting together or at cross purposes. Even when you have a lot of detailed information on a historical event it takes a lot of work to understand exactly why some outcome was achieved vs. some other outcome, and it's very easy to ignore all of that and think of history as inevitable or happening within some constraint of a larger purpose or larger system.