Amane's line on page 6 was actually changed in the manga compared to the light novel.
In the original light novel, it was "ああ、好きだぞ" --> "Yeah, I love it/them/you" (no subject). Contextually, it's clear that Amane refers to the egg pudding, but no subject is explicitly stated, so it can also mean "I love you," which is why Mahiru freezes at this. Note that Amane doesn't mean it that way.
This manga chapter changes this scene slightly. Amane's comparison of store-bought pudding to Mahiru's homemade pudding is a new addition, and his reply was changed to "真昼が好きだぞ," which unequivocally and irrefutably translates to "I like/love Mahiru."
From context and what we know regarding how the scene is meant to play out, we can infer that Amane meant to say "真昼のが好きだぞ," which would translate to "I love yours, Mahiru," to tell her that it's less that he loves pudding and more that he loves Mahiru's pudding. Amane doesn't realize his slip of the tongue, however, and Mahiru knows what he meant to say, so while she is surprised and freezes for a moment, she doesn't bring it to his attention. (To be clear, this is our conjecture)
Incidentally, this scene was skipped in the anime. Also, the exchange was butchered in the official translation of the LN by Yen Press, as it was translated as "You really do love eggs, don't you?" --> "Yeah, I do." which completely removes the important nuance that Amane's reply can also be taken as a love confession, which makes it look like Mahiru gets flustered over nothing. A translation akin to "Yeah, I'm in love" would have better conveyed what was going on.
