See: Ultra sensitive detection of radio waves with lasers https://www.nbi.ku.dk/english/news/news14/ultra-sensitive-de...
It would be interesting to see how this method of EM-wave detection interferes with the GW-detection.
1. At the LIGO observatories there are numerous auxiliary sensors, including radio receivers, that are used as "vetoes" for candidate gravitational wave events.
2. For binary black hole or neutron star inspirals, the gravitational wave waveforms are well-modeled using numerical general relativity. The fact that the observed detection matches the prediction so well lends additional credibility to the detection.
Regarding #2, we are of course hoping to detect something unexpected, with an unknown waveform. In those cases we'll rely on the veto channels to ensure that we have not detected contamination from a radio event.
Regarding 1: In the article, they describe an antenna that is MORE sensitive than the normal antennas. So you may not be able to detect the low frequency radio-waves without a similar sensitive apparatus.
Regarding 2: There is the problem that Electric signals can have high similarities with the "Chirps" that LIGO is looking for. For example: even in space, you can find all kinds of "chirps" caused by solar plasma. google "noises from space".
2. This point is valid.