confused about “…I may have tripped over someone else who's hiding”

I'm translating a post about psychology and having trouble with this sentence:

"I know when I'm sitting across from someone who's smiling brightly at me while simultaneously describing a significant loss or disappointment that I may have tripped over someone else who's hiding."

The context is someone trying to hide their negative emotions. But I can't say for sure what exactly the author is meaning. I understand what is meant by someone who's smiling brightly but it's the latter part of the sentence which confuses me, i.e. while simultaneously describing a significant loss or disappointment that I may have tripped over someone else who's hiding.

Does the author mean while he/she is chatting with someone who's smiling happily, someone out there is having trouble and stuck in sadness but trying to hide these emotions?

Or he/she means, he/she talks about an unhappy one while chatting with the bright one?

Could you guys please clear up this sentence for me? Thanks so much.

Solution 1:

When someone underplays or makes light of a traumatic episode in their life by smiling or cracking jokes, they are using a self-preservation mechanism as a means to display a stronger image of themselves to the outside world.

Thus the smiling person described in the excerpt is the same person protecting the wounded self, the person too afraid to come out in the open. The therapist realizes they have stumbled over the person who is hiding.

self-preservation instinct
the fundamental tendency of humans and nonhuman animals to behave so as to avoid injury and maximize chances of survival (e.g., by fleeing from dangerous situations or predators).

American Psychological Association