Is that a US-specific number? World Bank stats put the percentage of global population engaged in agriculture at ~26% in 2023

It's about right for any developed western country.

Because we import the agricultural products we consume from other countries?

No because mechanization has made farming require far fewer people than in times past. The US and many western countries export more than they import.

Mechanization and chemicals (fertilizers, pesticides, herbicides and fungicides).