Interesting article and a nice bit of detective work.
I came across something similar back in the 90s, some FM radio stations that I believed were unintentionally getting into the uplinks on two satellites.
I used to listen to analog single channel per carrier radio feeds via satellite. Tuning around on Ku band, I came across two groups of terrestrial FM radio stations. One I think was from Baltimore, and the other was from Portland, Oregon.
There were about 5 FM radio stations from Portland. It was frustrating listening to them though, because over a period of an hour or so, they would individually varied all over in signal strength, from full quieting to almost unreceivable. There were 3 things I noticed about these signals:
The frequency spacing between the stations on the satellite downlink was the same as on the FM broadcast band.
They were in multiplex stereo, which wasn't normally used on satellite SCPC signals.
The 5 FM stations in Portland were all co-located at the same transmitter site.
I guessed that these stations were getting into the block up converter of a nearby uplink and getting heterodyned to the uplink frequency. They were around for quite a few months. I was kind of surprised it lasted that long.