I agree with the statement.
The political parties are part of the governmental system. They seek to influence government policy from the inside. A pressure group tries to influence the government from the outside. They do not stand for elections or aim to become members of the legislature/ government.
Political parties have a broad agenda. They seek to represent the people for political, social, economic, cultural, and other concerns. Pressure groups usually have a narrow focus. They focus on specific issues or agitations for a specific cause e.g., the environment.