Cell phone mystery

I received an MMS in my office issued cell phone. It was addressed to me and another office mate. The sender that appeared was just a number. From its contents, I believed it came from our Vice President. Maybe, he used his other phone. So, I took note of the message.

When the sender of the MMS and I met, I asked him if he was actually the one who sent the MMS. "Yes", he said. "But, that isn't my number", he continued.

He showed me the sent MMS in his phone and it's recipients.

So, who owns that mystery number?

To solve the puzzle, I called it up. A man answered. I gave my first name, requested for his name, then asked if he's affiliated with our company and if he sent me an MMS.

His name doesn't ring a bell; and, he gave negative answers to my questions.

So, how it happened?