It says things like:
“We were not creating a lot of garbage.”
... but that statement there doesn’t say anything about the heap size, including the size and count of live objects (i.e., not garbage).
It also says:
“There are millions of Users in each cache. There are tens of millions of Read States in each cache.”
Large is often in the eye of the beholder, but I missed it if it said anything specifically about not having a large heap size.
Not sure why you got downvoted, you're actually right, I'm wrong: I misread that and/or assumed one meant the other.
That said, this is a case that should be ideal for generational GC, which Go specifically eschewed at one point. I'm not sure this is still the case, however--I have yet to wade through this[1] to update my knowledge here.
EDIT: Actually, no it didn't, I misunderstood it.