The classification of particles as matter or antimatter is not based solely on their electric charge. The concept of matter and antimatter is more fundamentally related to the particle's quantum properties, such as its quantum numbers and behavior under certain interactions.
In particle physics, every particle has an associated antiparticle with the same mass but opposite charge. Antiparticles have opposite quantum numbers compared to their corresponding particles. For example, the antiparticle of the electron (a matter particle with charge -1) is the positron (an antimatter particle with charge +1).
The up, charm, and top quarks, despite having a positive electric charge of +2/3, are still considered matter particles because they possess other properties consistent with matter. These properties include their quantum numbers, interactions, and the way they contribute to the overall structure of matter.
In the Standard Model of particle physics, matter particles, including the up, charm, and top quarks, are associated with left-handed particles, whereas their antiparticles are associated with right-handed particles. The distinction between matter and antimatter is based on the chirality (handedness) of the particles and their interactions with the weak nuclear force.
In summary, the classification of particles as matter or antimatter is not solely determined by their electric charge but rather by their overall properties, such as quantum numbers and behavior under interactions. The up, charm, and top quarks, despite having a positive charge, are considered matter particles based on these other properties.