Hey there!
The first part of Austin's reasoning is defintely correct. If you think of a circle with four parts and one shaded, you'll definitely know that's less than a circle with two parts with one shaded.
Now, we look at his claim of 3/12 being less than 1/12. Let's look at the factors in 3/12:
3/12 = (1)(3)/4(3)
Cancel out the 3's to get 1/4. Now, we know that 3/12 and 1/2 are the same thing. Therefore, Austin's reasoning is correct.
Hope this helps!