It's not about assumption, it's about experience, visual analysis, and providing an informed judgement. Interesting specimen? Sure. Meteorite, no. I'd agree about the possibility of an impactite, they come in wide range of appearances and compositions. I also wouldn't exclude the possibility of a terrestrial conglomerate, though it does more resemble a breccia. Lab analysis can be definitive, but unless it's a geology or meteoritics lab, done by someone with experience with meteorites, it's just another opinion. Contrary to statements in previous posts, not all meteorites contain nickel, iron, or any metal at all. Most do, but certainly not all. Here's a useful analogy from machine learning. You can 'teach' a computer to determine if a character is a letter 'A', by running it through an algorithm that assigns the expected characteristics of an 'A', or, you can 'show' the computer thousands of examples of 'A's and with the proper programing, allow the computer to 'learn' how an 'A' may appear. The latter method proves to be far superior. Keep this in mind when dismissing a judgement made by someone who has handled tens of thousands of genuine meteorites, against an analysis that shows commonality in elements, compounds, or minerals between terrestrial rocks and meteorites. Form matters.