As in a previous comment, the blood drive can have social aspects but the core of the event is not to socialize but to provide service. You can socialize by happenstance but it does not make the venue a hub for socialization.
You can go to a restaurant to just eat or you can choose to dine with friends.
The key is to highlight what activities related to the specific restaurant nominated is great to do there if we’re talking about the socialization eligibility. As in you take peers and stay there to socialize kind of thing.