Triac wiring section
Excluding government regulations, the two factors to consider for low-frequency copper conductor cross-section are acceptable voltage drop and acceptable temperature rise. The house wiring consists of very long wires. The triac lead and PWB traces are very short and they should have a good thermal path to keep the temperature rise down.

Tables showing maximum allowed current for various PWB trace widths are only considering temperature rise. The PWB traces right at the part may need to be narrow, but you should quickly increase the width to as large as practical.