Purchasing a good or service with multiple components is not, in and of itself, a representation to the seller of intent to use all the components.
Now, there could be something United has inserted in the purchase flow of all multileg tickets which assures that the purchaser makes a representation of intent to use every leg, though I've never seen anything like that when purchasing tickets (and a contract of adhesion that United writes that most purchasers will not read, while it may succeed as a contract, probably won't be seen as such a representation for fraud purposes, AFAICT.)
Now, there could be something United has inserted in the purchase flow of all multileg tickets which assures that the purchaser makes a representation of intent to use every leg, though I've never seen anything like that when purchasing tickets (and a contract of adhesion that United writes that most purchasers will not read, while it may succeed as a contract, probably won't be seen as such a representation for fraud purposes, AFAICT.)