As per the founder in the thread:

Once the Phase I trial of PVX-001 concludes, we will open-source the design and manufacturing information needed for others to produce and build on it, and we will not enforce our intellectual property rights against anyone who uses it to make vaccines against any betacoronavirus [...]

The headline seems slightly inaccurate. A pledge of later going open-source isn't the same as open-source. Sure, "marketing".

Hey, it worked for OpenAI!