The conclusion:
"This is the first directdetection of gravitational waves and the first observation ofa binary black hole merger."
Both of these assumptions are based on the assumption of each others existence, and on theoretical assumptions on their properties. From a scientific point of view it is incredibly weak evidence. It is like measuring vibrations in Loch Ness and assume a particular vibration could only be from Nessie burping. Thereby proving that Nessie exists and burps, and that the vibration measuring device is a valid method to measure it, without ascertaining with any complementary method, photographic evidence for instance...