Dude (m/f), don't drive after donating blood. Go with a friend or take public transportation. You're a risk to others, too, especially if you don't donate regularly and don't know how you'll react.
Yes, you are absolutely right. In this case, there was a mobile collection unit in the office parking lot. This is very common where I live. Sorry for the confusion.
They park donation vans outside of office buildings, it's probable that's how he donated.