But even if it did send HEIC, if you're going to fail to handle "any" format, then you better specify the one you can handle. By the same token, why shouldn't my computer convert every .docx to PDF, or some other "more universal" format?
Instead of specifying the requirement programmatically, they spent their time sending out tweets and writing help docs.
Point of order: separate people, with separate/independent/concurrent job responsibilities. It very likely wasn't the programmers tweeting and writing docs. (Heck, I expect that the College Board doesn't even retain any full-time programmers, only contracts with firms for projects.)
It's the same as if Apple shipped me an empty box instead of my iPad Pro. Of course I can't blame the customer support person who takes my call, and I shouldn't be rude to them. But I would still blame Apple the corporation for such a thing, had it happened.