You're observing shamefully bad journalism. The "protect Earth from aliens" bullet point in the "Highlights" section of the article was put there by an editor who either ignorantly or willfully distorted the actual role of the Planetary Protection Officer.
The first paragraph of the story gets a little closer:
The full-time role of "planetary protection officer" will involve ensuring that humans in space do not contaminate planets and moons, as well as ensuring that alien matter does not infect Earth.
"Planetary Protection Officer" isn't a new position; the current one is retiring. The primary focus of the planetary protection office is sterilizing probes that are going to other planets and moons. This is done both to preserve any existing life elsewhere in the solar system from Terran competition, and so that if and when we find life on other bodies, we will know we didn't bring it ourselves.
Preventing microbes from other worlds reaching Earth is also a concern, for similar reasons.
Developing and implementing the policies of the planetary protection office is a complex job requiring a broad array of both technical and human skills, and so a $187K salary is not remarkable for it:
Candidates will be required to travel frequently — but like any job, there will be a significant amount of emails, proposals and other reading.
Candidates must have at least one year's experience as a top-level civilian government employee, and an advanced degree in physical science, engineering or mathematics. They must also have "advanced knowledge" of planetary protection.
The position also requires "demonstrated skills in diplomacy that resulted in win-win solutions during extremely difficult and complex multilateral discussions". The new hire will also receive "secret" security clearance. Only US citizens and US nationals can apply.