Strangely enough, this is the only real stalker-y thing Matoi does.
I mean, yeah, the three-steps-behind-you-at-all-times thing and that sleeping underneath your bed bit is a trifle extreme, but at least she's not outright threatening your life or anything. Nozomu's actually on a conversational level with her, for crying out loud.
Besides, if you had a stalker, and she looked or sounded anything like Matoi, would you really mind? Like, at all?