If you grow it, and you don't poison it, it's edible. The MIcrogreen brand of sunflower seed is sold specifically to grow edible greens. What makes you think it might not be edible and only for birds?

The most common type of common sunflower (Helianthus annuus) for micro greens is oilseed sunflower used for making sunflower oil. The seeds are also used as bird feed since they are meatier and have a higher oil content, giving birds more nutrition. Seeds of all varieties of Helianthus annuus are edible to humans.