My boy had a similar experience with what's been posted here...
Some coding job interviewed him, asked him to complete an assignment, he replied back with some pdf with a watermark on it, only posted half the code... They replied back and asked him to send the rest, he was like "nah I can go to your office and interview, write up the rest of the code and show you it will work within your system, you can evaluate it and tell me your decision" they never replied back

I don't know much about IT security or coding, but he tells me this is a common tactic to get an outside view on certain issues.