The Refugee Convention does not require refugees to apply for asylum in the first safe country they enter. It allows them to seek protection in a country of their choosing, often based on family ties, language, or historical connections. Many asylum seekers in Calais have family in the UK, speak English, or have ties to former British colonies.
Wouldn’t you do the same if your family were in another country? Seeking asylum where you have support systems is logical and human.