What you did would be fine for a commercial report, or an internal memo. In that case you are just looking for the best information you can find, and Wikipedia

What you did would be fine for a commercial report, or an internal memo. In that case you are just looking for the best information you can find, and Wikipedia is as good a source as many so it can be part of the research. But you're not understanding academia when you lump Wikipedia in with other sources. The purpose of publishing is not just to write down what you have reason to believe. The purpose is to build up a verifiable chain of trust. It's a lot like a block chain actually. When you publish in Nature, and note that you are employed at Stanford, what is happening is you, Nature, and Stanford are all "signing" the paper. Then when someone cites you, they are building on your chain. That allows you to read a paper published somewhere and be able to rely on its truthfulness, to some degree, without manually verifying each source. Part of what you learn in academia, what your professor was trying to get you to learn, is how to write a paper which could be published. If you cite a Wikipedia page, that can no longer be published because there aren't enough "signatures" on it to verify a chain of trust. Yes, you can verify it by hand, but that doesn't scale. The point of scholarship is to scale verifiable knowledge. It's a little sad your instructor capitulated. It's possible they realized you were in a professional program and you weren't supposed to learn how to do scholarship... that your task was just to be able to write a professional research report, and for that Wikipedia is fine. It's also possible they assessed that they're not being paid enough to argue with indignant students and gave you the grade that would shut you up. But regardless... you should know that what you did is not scholarship. That requires you to participate in the consensus algorithm and the verifiable chain of previous work.