What is a “part-key”?
This example does not contain a partial dependency to me.

A partial dependency would be if a table column functionally depends on part of the table's primary key, like in this denormalized table:

CREATE TABLE student_activity (
   studentid bigint NOT NULL,
   activity character varying(30) NOT NULL,
   fee numeric(10,2) NOT NULL,
   PRIMARY KEY (studentid, activity)
);


where fee depends on activity.

The solution would be to split this table in two parts like in your question.