Yes—if the focus ring has developed any grinding sound or gritty feel after a dusty trip, it’s wise to have the lens inspected and cleaned by an authorized Canon service center.

“Weather resistant” does not mean dust-proof, and manufacturer sealing claims can be limited in real-world conditions. Dust intrusion can happen even with higher-end gear. Since the lens is still functioning, it may not be an emergency, but grit in a moving mechanical part is something to take seriously rather than ignore.

A professional cleaning is mainly justified here because of the new grinding sensation in the focus ring, not simply because the camera was used in a dusty place. If there were no symptoms, routine external cleaning and monitoring would usually be more reasonable. But with audible or tactile grit, service is the safer choice to help avoid wear or further contamination.