You act like there's no latch on the inside of the hood that holds it down. When you pop the hood on a 300ZX, you have to unlatch it to open it (I expect you already know this). If you hood flew open as it did, your latch wasn't doing something right. And you know what? I've never heard of a stock hood doing that.
Putting eBay "performance" parts on your Nissan 300ZX is like putting Pep Boys wheels on your Cadillac Escalade... even people on welfare know better.