NP; Good as Gold

[Mike Jing]

I'm puzzled by the word "credulously" in the following passage:

Several questions rose simultaneously in Gold’s mind and broke into pieces
against each other in the burbling struggle to get out. “Together? Found
out? How? How together? Are? What do you mean found out? What do you mean
together? How are we together?”
“Like this. He knows all about us.”
“Knows all about us? How did he find out?”
“From the children.”
“From the children? How do the children know?”
“I told them.”
Gold looked at her steadily with a troubled eye. “You told them? You told
your children? What did you tell your children?”
“That we’re lovers.”
“Lovers?”
“You keep repeating everything I say.”
Gold was lacking the necessary equilibrium for timely repartee. “Is that
what we are, lovers?” he asked credulously.
“Of course, darling,” answered Linda with a smile. “I’m your lover and
you’re mine. What did you think we were?”
Gold did not hesitate long to give the answer that first sprang to mind.
“Fuckers.”
“Lover is so much sweeter,” said Linda Book with the ethereal sensitivity
of a poetess, “so much richer in meaning and value, don’t you think?”
“Don’t you have to be very seriously in love to be a lover?” asked Gold.
“Oh, no,” she corrected him. “All you have to be is a fucker.”

I can't quite make sense of it. Shouldn't it be "incredulously" instead?