Read the article? “NASA’s Parker Solar Probe and the European Space Agency’s (ESA) Solar Orbiter, when they coincidentally lined up to observe the same solar wind stream…” They both happened to capture data about the same event, which allowed them to combine the information to get better data. It’s not weird that they collaborated, but it was unexpected that these two missions did in this case.

What’s unexpected is that they didn’t plan the collaboration years in advance.