It means that to do variable sized things like vectors and strings, C++ often ends up having to allocate their contents dynamically. Which results in data structures with lots of 64-bit pointers over multiple allocations.

Even Rust's "enum" feature, which can store different sized things all in the same space, does that at the cost of the smallest variant being just as big as the biggest.

Goose can do all of that not only inline (no pointers), but with variable size, meaning small items take less space. It's like a serialized data representation, but iterable. It makes for big space savings vs these languages.

I parsed it as "A record that is ((160 bytes and an allocation) in C++) is ((29 bytes and none) in Goose)."

So, I read it as, "C++ uses 160 bytes and an allocation, when Goose requires 29 bytes and no allocation".