As a professional actor, what Lin Yun was best at was grasping the psychology of others.
Psychology and behavior must match the character's background to avoid blowing one's cover when undercover.
Even if one did something that didn't fit the character, as long as the thought process was there, the character wouldn't be considered compromised.
So, what was the mindset of Comrade Xiaohai, who was fished out of the sea, when she uttered that sentence?
She was confident.
She believed in her own strength, convinced she couldn't repay now but certainly would in the future.
But as someone with amnesia, where did that confidence come from?
Clearly, she lied, or maybe, she hadn't lost her memory.
She didn't have amnesia yet told him she did, which meant she couldn't reveal her identity. There wasn't enough time to react and concoct a flawless identity, so amnesia served as a disguise.