Assuming the FAA has the authority to enforce ADSB requirements (an open question post-Chevron), I can’t find any regulation saying non-aircrafts cannot transmit ADSB. Only ones saying aircrafts in certain categories must.
There’s probably some non-interference requirement somewhere (FCC spectrum licensing perhaps), but I’m not seeing it immediately.
All this is in the hypothetical that RF was transmitted, which as others point out it probably wasn’t.
Whatever transmitter you're using would not be type-accepted for operation on the 1080 MHz or 978 MHz band. (47 USC § 301)
Additionally, RF operation with the intent of willful interference is inherently illegal. (47 USC § 333)
Also does impersonation necessarily qualify as interference? Naively, I'd expect interference to refer to jamming.
This is easily-prosecutable willful interference or possibly aircraft sabotage: ADS-B operates in licensed bands and uses an already highly-contended modulation scheme and transmission protocol.