Typically, only the accountholder's income would count, not the authorized user's.
If it was a joint account, both would count.
Some lenders count combined household income in cases where the account holder lives with another (their spouse, fiance, partner, etc).
After all, when you authorize a user on your account, you are the one making the credit decision - you deem this person worthy of extending use of your credit to them. The lender isn't involved. You as the primary account holder are the one who is ultimately responsible for any use of the card.
In a joint application, the lender is the one making the determination of who deserves credit - and both parties are liable for the use of it, individually and together as a pair.
In cases where they consider combined household income, they are weighing just your creditworthiness but using all money available in the household to determine how much credit to extend you - since they assume you are free to comandeer any of it necessary to pay your bill. The liability for the use of the account still belongs only to you as the primary card holder.
An authorized user gets a card that is linked to the primary account, and is free to use it but bears no real responsibility for the bill as far as the lender is concerned, so the lender has no use for that person's income information (unless it counts in a combined household income figure where those are used).
