If Blender was a company, to get access to the technology Facebook would have to buy it by hundred of millions of dollars. But it is a open source project, so they could just take the source code to develop a new program. However, it is clearly more convenient to support the current Blender project with a small funding rather than to create a full new department of engineers with a significant budget to deal with the code.
It is not related to "get access to technology" as the open source nature of blender already allow it.
It's a tax advantage + brand image operation - ridiculous small fund compared to FB power -, not certain it will help that much blender as FB behavior arouses many haters.