Perhaps he is interested in the food as he is interested in the pot holder, the cooking spoon and so on.......
Food is yet another thing to investigate and learn about in his new world. Even if that means tasting it and spitting it out, or just squishing it between one's fingers. He may not neccessarily be interested in 'chewing' and swallowing it, or associate it with a full belly. He may be seeking something to teethe on and that celery may feel good to his gums.
My son was reaching for food early but we didn't start him until eleven months. Even then, it was the novelty of something new. He quickly learned to spoonfeed himself then once it became common, he was less interested.
I personally think you should just go with your gut, if you feel you should offer him something and he takes it right away and pops it into his mouth and chew/gums it then swallows, then he probably is interested in eating as well as ready. Chances are he may just play with it, perhaps gum it then spit it out. Who knows though, it should be easy enough to find out so long as he is actively making the choices and taking the action.
Basically I feel if a baby is advanced enough to sit up and grasp the food, then put it in the mouth, gum/chew then move the food to back of the mouth to swallow, baby is pretty much ready in my eyes. That to me is baby making the choice and taking the action versus being pushed to eat food before physically ready. Not that you would do that 
I am just making a comparison!
