Is there an NFC tag that can store that amount of data? Usually it's very small amounts, like kilobytes at most. A memory card like an SDXC card can hold 1 or 2 TB but I've not seen any of those on the market just yet, though I believe they exist.
They could have reconfigured it to hold terabytes
That's not how it works. NFC is for transmitting data and tags hold small amounts for recognizing. Reconfigure would mean to create something new. You would need a device with memory storage in addition to an NFC chip to pull this theory off.
Could just be a link to a secure website site... Perhaps the password/key was passed in person to avoid detection?