It's in your best interest to take a step back and really try to be in your coworker's shoes. There's many unknowns that explain everything.
Despite your frustration, it's still not professional. You don't know what's going on. If you cannot empathize you're unqualified to be a software engineer and should pack up your stuff. It's not about you or a silly project everyone will forget about in a few years. Your coworker may be making up excuses because they don't want to share what's really going on with the rest of the team, especially if the other members are poking around. A close family member might be sick for all you know and management has enough heart to let their performance slide.