I'm German and that is bullshit. Never heard of mäusespeck, everyone just calls them marshmallows and they are labeled as marshmallows in the store
EDIT: I was made aware that the Problem seems be that im not a boomer. 30 years ago, when i wasnt alive, they seemed to be called this. In my WG there are people over 30 though and they also never heard of this (hessen)