No, Kubo-san, it's not his fault, it's yours. For the life of me, I don't understand why she just won't tell him she gave him the Valentine's cookie. She knows he's denser than a block of coal, as well as being outstandingly socially inept. It's like she wants to inflict him with more social anxiety pain. From what you told him, "Don't worry, I'll make sure to pass this along", he'd be even less likely to think you're the one who gave him the cookie. Frankly, she deserved that little heart attack when she realized that he didn't know she gave him the cookie.