It was one event, a neutron star merger. The gravitational waves were emitted during the inspiral, the light was emitted as the neutron stars smashed into one a

It was one event, a neutron star merger. The gravitational waves were emitted during the inspiral, the light was emitted as the neutron stars smashed into one another and then blew apart in a "kilonova". The two weren't emitted simultaneously, there was a slight delay between the production of gravitational waves and the peak brightness. However, the important aspect is that MOND theories predict not just a slight difference in travel times but literally months or years worth of delay.