Ok so, at best, it's a lazy and thoughtless gift - he picked it up at the airport on the way home in a panic because he hadn't thought to get you a gift earlier. Kind of along the lines of, as they're getting to the last call for boarding, 'Ooo quick! I know, London likes chocolate and that looks ok, especially if I buy loads.'
At worst, he's trying to sabotage your diet and undermine your confidence at the same time (depends on exactly what he said about being too fat for the dress and whether it was in response to being asked etc).
But there can be all kinds of other stuff happening behind this. How is he with you being confident, doing things independently, having success outside of the home?
Does he have a thing for fat women? I know someone who cheated on his DW at the end of a diet when she'd successfully lost 3 stones - the OW was about 2 stones heavier than DW had ever been (pregnancy aside).
My DH was brought up to think that food is love. He shows love by bringing food treats and making 'treat' ie unhealthy meals. My family was the same. DH feels hurt when his food is rejected. We talk about it openly but he still does it. He is much better at hiding his disappointment if I say no thanks.
It's a wonder we're not all enormous.
Or it might be nothing but a silly mistake. I'm just interested because of the food dynamic in my family. What's he like usually?