I don't think the "UI Toolkit" Flutter you know today was from an acquisition. Eric Seidel (leading the Flutter team at Google) mentioned in a video that they needed a name for the project and they used a name from one of their acquisitions. As verifying that a name is available in most important countries is expensive and time-consuming, they just went through their internal database of available names and this is how they picked Flutter. I couldn't find a link to the video right now.