the key word is "mixed together".
It's not "bread" if it's not mixed together but separated.. or rather it's "bread with X".
Curry buns are actually filled with curry. So it's not mixed together.
Melon bread on the other hand can be considered bread, although we Germans wouldn't eat it as such, but consider it a snack... but I'm sure asians don't put anything on it either.
In Germany we have "filled bread" as well, it's rather new, but it's not bread. "Handbrot" for example.
I guess the closest, but still different to actual bread would be "Kräuterbaguette", which is basically a variation of garlic bread, directly translated it means "herb bread/baguette" but I'm not sure if that's actually a thing elsewhere?
Either way, if you ignore the mixed together part:
You may as well call a wellington bread, or crossaints bread if you consider curry buns as "bread"
Or Pizza, which includes bread, but isn't classified as "bread"-bread. If that makes sense.
Btw... I've never tasted Melonpan, but what I THINK they'll taste similar to is
"Streuselbrötchen".
Which is awesome soft, sweet bakery in form of Brötchen/bread, which are snacks.
And then there is Milchbrötchen, which is different but also sweet and soft, but also just a snack.
edit:
If I'm not mistaken, to be considered bread, you are actually only allowed to have X% amount of fats and sugar vs wheat ratio. Something like that.
That's why crossaints is pastry and not bread, too much fat. (Same with donuts)