How can you tell if a particle has been created with VFX Graph rather than with the Particle System?

The option indicating that double-clicking on a VFX Graph object in the Project window opens it in the VFX Graph window is correct because this behavior is a clear indicator that a visual effect was created using the VFX Graph. The VFX Graph is a distinct tool within Unity designed for creating complex visual effects with a node-based interface, and its assets (VFX Graphs) can only be opened and edited using the specific VFX Graph editor. This characteristic directly differentiates VFX Graph effects from traditional Particle System effects, which do not have this specialized editor.

Other choices may not reliably confirm the creation method. The presence of a Particle System component is a definitive sign that the traditional Particle System was used, while additional factors like color options and custom shaders might also appear in both systems depending on usage and design. Thus, the ability to open the asset in a specific editor is the most straightforward way to identify the method of creation.