The artist's commentary says that he thinks Nagato's English voice actor sounds particularly erotic in this scene.

...I can't say I necessarily agree with the erotic part [though now that he mentions it...] but Michelle Ruff does a good job regardless.

This is probably a good chance to rewatch Haruhi since I haven't watched the original in years and I've never watched the dub.

The artist specifically mentions the... "lisp" isn't quite the right word, but there seems to be something of a speech impediment with her pronunciation of the consonants "l" and "t".
The artist seemed to fixate on the phrase "all of it" but for me it was more noticeable when she says "A little." I wouldn't have called it erotic, but it was downright adorable. Almost childlike.