What secret does Peeta reveal at the end of his interview in The Hunger Games?

In Chapter Nine, when each of the contestants of the
Hunger Games are interviewed, it is Peeta that is last, and it is Peeta that manages to
steal the show by his confession of love for Katniss in front of all the cameras and
Katniss herself. Note how the chapter ends with this revelation, that is a surprise to
everyone, most of all Katniss. Having been asked why his love is so impossible, Peeta
responds:

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Peeta blushes beet red and stammers out.
"Because... because... she came here with
me."

This of course gains
them both universal sympathy and support, as impossible love situations always manage to
engage the public and the media. However, at the same time, as we consider the personal
drama going on between Peeta and Katniss, this leaves Katniss very unsure of what is
happening, as she doesn't know if this is just a cynical ploy of Peeta's to gain support
for him or if this is genuine.