That certainly exacerbated it, but arguably it's not even the worst RF sin being committed here. The other is spurious emissions. Toggling a GPIO at frequency f

That certainly exacerbated it, but arguably it's not even the worst RF sin being committed here. The other is spurious emissions. Toggling a GPIO at frequency f doesn't just result in frequency f, it also results in 3f, 5f, 7f, and so on because the GPIO is outputting a square wave not a sine wave. That's the best case. Unreliable timing could turn that from a frequency "comb" into a forest of spurs across the RF spectrum, and whichever spurs make it out of an antenna are going to break the law (best case) or interfere with important RF devices (worst case).