While it sounds like the College Board may be at fault for some of the issues, like the test timing out when HEIC images were sent or the initial communication of the issue, I wouldn't be so quick to place all of the blame on them. Part of the problem is how we more-or-less glorify an ignorance of technology. This can be seen in both students trying to change the file type by changing the file extension and JPEG being referred to as a "most compatible" rather than by name in the settings.
EDIT: the comment about "most compatible" was based upon information from the article, rather than access to an iPhone. I have since looked it up, and JPEG is mentioned underneat the option.
I am saying this because people need to have a degree of understanding of technology in order to have some control over it, even though I recognize that some people will construe such statements as being elitist. That depth of knowledge does not even have to be particularly deep. In this case, understanding that photos may be represented in different ways by the computer and that you have to ensure that the recipient can accept that representation is important. After all, this is not the only case where they will run into this issue. It is a big part of the reason why businesses settle upon some form of standard for the exchange of data, may that be through common business practices or a standardization body.