Unlike GA, Facebook Pixel is not bound to a device, in other words, its user-based, and tracks everyone who logged into Facebook and clicked on your ad.
GA utilizes a completely different approach. It’s cookie-based, which means it tracks interactions based on devices. We’re not trying to bash the mighty GA here, however, what if your lead tapped the ad button while using a smartphone and then proceeded to your website via PC? GA will track it as two different interactions.