Short answer
Yes, a small amount of chia seeds is safe for a puppy. Always soak them first because dry seeds can swell and cause a choking hazard. Offer it mixed into his regular wet food and watch for any digestive upset like diarrhea. If he seems uncomfortable, check with your own veterinarian.
Chia seeds — Food safety facts
Safe to share · Dogs · full breakdown on the linked food page
Safe when soaked or mixed into wet food. Dry chia swells and can block the throat.
The full verdict, portion guidance and serving notes are collected on the Chia seeds food facts page.