Hi! I think that the most important concept behind a vCard should not be the card itself, but portraying a (virtual) personal identity. In this way, when we represent only the persona shape instead of the card we make strong emphasis on this.
Second, and I paraphrase from the blog post, "using a circular container has its constraints, and trying to adapt a rectangular design in a circle is something problematic, specially by correct use of the available space and margins". This also was a driver towards the current circular shape.
Last, the at(@) symbol is crucial for the link between communication and virtuality, and also to separate this to the classic "user" shape.
Had you already decided that the @ was important? In which case, what is that diagram trying to show? The final icon, while quite nice, doesn't represent "vCard" to me because it's too focused on email rather demonstrating what a vCard is - a representation of all of the things a user might have available.