It is comparing being duped to the imaginary but descriptive scenario of invited to someone's house for lunch and seeing an assortment of delicious looking food on the table, but then, upon being served, discover that it's only very realistic-looking playfood. It looks delicious, but it's a toy, a prop, only fake, nothing you can really eat. Similarly, if someone makes you a tempting offer that turns out to be phony, it too looks great, but it's nothing you can really act on, it's only fake.
"Suzanne, I want you to stop talking about marrying Carlos. Carlos doesn't want to marry you, OK? He views your relationship as a break in his routine and nothing else. When he talks about you two having a life together, he's just serving you playfood for lunch!"
"All the companies that offer instant weight-loss products are serving the public playfood for lunch."