It's just fine for a news organization to have its own style, applied consistently. But Mr. Rewrite must point out to students and the broader Community of Concern that this is a departure from Associated Press style.
Per the stylebook entry on hyphens (punctuation section), hyphenate compound modifiers to avoid confusion (example: small-business man) and avoid hyphens when possible. The entry lists health care center to illustrate when a hyphen doesn't help.
As for social media, the stylebook entry on social media optimization (no hyphen) is a guide: no potential confusion, no hyphen.
Mr. Rewrite prepared this on his iPhone as Rewrite Jr. played in a bounce house. Is that a good thing?