Any snake can get constipated if they get dehydrated, What are your temps and more importantly, humidity. I keep my boas between 70-85% humidity. Was the chunk white as in urate or actually brown/black like a poop?
And if you feel a lump down by his vent, then i would say yes, he's constipated.
Soak him for about 30 mins in a barely warm to the touch tub of water and gently massage the spot and see if he poops. But the bottom line is you need to get his humidity up if it isnt. Curing the problem is one thing but you need to find the cause of it so it doesnt come back.
And it was the size of a chicken egg from an 11 month old??!!! I find that a bit of an exaggeration as the width of the large rats my 6.5' girl eats are about as big as a chicken egg. My one year old salmon boy is maybe a little thicker than an adult mouse.