shortly after the bigbang, when the universe was a nonzero amount of time the size of a potato, compared to its current size, how to reconcile that with 'it doesnt expand into anything'?
Because the universe follows general relativity, space itself behaves like a fluid. When the universe "expands", that's just space itself growing bigger over time.
Note the Big Bang is a point in time where all paths started, as stated in the article. It’s a mathematical singularity. It’s not an explosion as you think of it. It was a sudden expansion of all points in space creating vastly more space between the points. But since space has no boundary it didn’t get bigger, and it wasn’t smaller.
This makes zero sense.