According to the FCC's notices linked on the page, they were selling at least 65 radios that weren't certified, and thus were illegal to sell. And 12 of those radios could transmit on frequencies the FAA uses.
Then they tried to ignore the FCC when it was investigating them, and didn't turn over all the information the FCC requested.
And then they made a bunch of bad arguments to try to get out of the fine. They tried to argue "no harm, no foul", since no one complained about interference. They tried to claim the 5th Amendment protected them (as a corporation) from self-incrimination, which thankfully is not what courts have said. And they tried to argue that they couldn't afford the fine, but didn't turn over financial records to support it.