I'm fascinated how you seem to know this to be true. While I've never seen a screwball, I've seen a million inside pitches that 2 time Olympic Gold Medalist Michele Smith calls a screwball. But that doesn't mean it did what she said. So, if she is misidentifying anything inside for a 'screwball' then it's easy to mischaracterize a drop as a "Fastball" , especially if it's not breaking sharply on that day or on that particular pitch. Plus, I'm guessing WCWS, primetime game, on ESPN, capacity crowd cheering, etc. would jack the pitcher up and create a lot of "over throwing" which makes balls stay flat: giving a drop less movement making it look like she intended for it to be straight.
I think Michele is being generous, perhaps looking at basic form rather than function. I have seen Yukiko Ueno throw curve-balls that corkscrewed and didn't move an inch. Just stepping left and throwing inside isn't a screwball to me, but most are exactly that. And that is why the left-field fence loves an over-used screwball.