when I wasn't able to complete all of the new aspects of my job to my employer's satisfaction I was fired.

You got approved for unemployment because you lost your job for "failure to meet expectations" and not wrongdoing, not because they expanded your job duties.

Sucking at your job doesn't disqualify you for unemployment. Violation of company policy or willful wrongdoing does. If you have an employee who is making a good faith effort to perform but just doesn't meet standards, like a salesman who is following the rules but missing quotas, they still get unemployment if they are fired.

In your case, they were free to expand your job description, free to fire you when you failed to perform, but since you presumably made a good faith effort to do the work assigned to you (even if you failed), you got unemployment.