I can’t find anything in the Communications Act of 1934 that gives the FCC jurisdiction over marketing practices.
IANAL, but Truth in Advertising[1] enforcement is a FTC affair, not FCC.
On the other hand, rayiner is, so there a benefit-of-the-doubt element that I'm inclined to respect.
EDIT: ...and I humbly stand corrected.
[1] https://www.ftc.gov/about-ftc/bureaus-offices/bureau-consume...
The "5" in "5G" is just a version number; it ticks up whenever someone decides they want it to.