With income of $5000 (plus $800 dividend), he is not required to file a return. Minimum filing requirements are $12,000.
If he was a full-time student for at least 5 months of the year, you can claim him as your Dependent and he can still file a return (indicating he was claimed as a Dependent) to receive a refund of any Federal Tax withheld on his W-2.
It could be that his father is filing the PFD 1099 on his return, which he is allowed to do.
Here's more info:
https://ttlc.intuit.com/replies/3302274