The criterion given is this:

"More than 10 accepted answers with score 0 and 25% of total."

Now I was going through my accepted answers and I saw that $$14$$ of my total $$40$$ accepted answers had score $$0$$, which is $$35\%$$ of total. Now I went ahead and checked who the system had awarded the last badge to. And that guy had $$12$$ of his total $$48$$ accepted answers with score $$0$$ which is $$25\%$$ of total. Now I think I am a "more" Unsung Hero than that guy. Even more so, if my next $$20$$ accepted answers are all of score $$0$$ which would make make my tally look like $$34$$ out of $$60$$ accepted answers with score $$0$$, which is $$>50\%$$ total. I think that is "more" Unsung, but the badge system disagrees with me.

Your thinking is not wrong. The problem is that those badge description are not complete in all details. Specifically:

There is a lower limit on the age of an answer to qualify (ten days).

Several of your answers are more recent than that. Restricted to those that are old enough you are at 8 score 0 accepted out of 26 accepted and you do not meet the "more than 10" anymore (while you still meet the percentage).

Note that self-answered ones don't count either and you have (at least) one of those, thus at the moment you are at 7 out of 25. CW would not count either but you don't have any of those.

For a sources that usually contains all the details on the badges see:

What are the badges I can earn on each site, and what are the exact criteria for earning each badge?