If you are talking about the definition of a particle, then that is something else. Likewise, we can say that about every single thing in this world. I'm sitting on a chair right now, but I am not sure if I can call a stone outside that people are treating it as a chair, a chair. If you are confused about the definition of a particle because you are confused about the distinction between a classical particle and a quantum mechanical particle, then we are talking about something else. You are perhaps confusing the difference between how things should be defined, with how things are. If not, then read below.
I'm sorry, but what you said in that post is wrong. In science, there is a specific term to express your description of particle: quasi-particle (in a loose sense. This term is actually used for solid or sometimes in molecules as well, but its definition seems to be rather loose and can be applied to others, recently.) These are actually not, particles, but "seems like" they have the properties of such, and are treated mathematically as particles, thus the term. Plasmon, phonon, exciton, are some of these examples. This is distinguished from actual particles, like the one we are talking about.
Also, an atom cannot be viewed with photon or any microscopes that utilize light source as probes (generally. There are several new methods like PIM (photoionization microscopy) and QEM (quantum entanglement microscopy) that utilizes photon in a very sophisticated way). This is because a photon has a large wavelength that exceeds the resolution of the material we are looking at. I said AFM (atomic force microscopy), TEM (transmitting electron microscopy) as well as STEM (scanning transmitting electron microscopy), STM (scanning tunneling microscopy), APT (atom probe tomography), etc. These probes do not use photon. Out of these microscopic methods, AFM may be the one that most accurately shows what atom should look like, since it is based on repulsion force that minimally interacts with an atom and changes its state, meaning it does not entail disruption of what we are trying to observe.
While you are right, and I agree, that the mathematical formulations of these particles are symbolic, these mathematical methods are chosen with precise care to make sure what we are observing is a real particle. Quantum mechanics works this way. So what we are observing is, in fact, a particle.