If he flipped the coin 100 times and got 50 heads, then the answer would be 0.5 (since 50/100 = 1/2 = 0.5). I think you might be mixing theoretical probability with empirical probability.
In this case, he got 28 heads out of 75 flips
so 28/75 = 0.373333... where the 3's repeat forever
This rounds to 0.37
That's why the answer is actually choice A