As other commenters noted, this is almost certainly not RF spoofing, just sending bad data to an aggregator (ADS-B Exchange) over the internet.
This instance of spoofing is notable for being the first that I know of that wasn't primitive vector art or text, but a raster image!
In that area of Florida multiple receivers would have picked up actual ADS-B broadcasts. ADS-B aggregators do have various anti-spoofing measures, but they're not impossible to circumvent.
The only case of actual RF spoofing of aircraft transponder signals that I know of was actually done by the U.S. Secret Service, which interfered with passenger jet collision alert systems (TCAS) by apparently broadcasting bogus signals near Ronald Reagan National Airport (KDCA): https://nymag.com/intelligencer/article/aviation-flights-whi...
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