I think this is misleading...
Because something is removed from RSTC doesn't mean that it shouldn't or can't be taught. It also doesn't mean they advocate or discourage it. RSTC establishes minimum standards that must be met for an accredited certification course. GUE, for instance, covers things not listed in RSTC, doesn't make them bad nor does it mean they are teaching against RSTC.
How does this relate?
If the AGENCY (not RSTC) removed it from their training standards and assert that nothing beyond the standards can be taught, then the instructor is in trouble. Whether or not I agree with it is a different story, but the conditional is legally important.
Whether or not it is RSTC does not, directly or indirectly, relate to the cause of the accident (rather, it attributes to legal negligence). Because this is a forum not intended to assign blame or legal advice, I don't think further discussion is really necessary (for this thread). That being said, I am interested in hearing the details of the skill being performed and the circumstances contributing to the incident, that is what is most important (at least here).