From their "Grin for Bitcoiners" article [0]:

    There are 3 main properties of Grin transactions that make them private:

        - There are no addresses.
        - There are no amounts.
        - 2 transactions, one spending the other, can be merged in a block to form
          only one, removing all intermediary information.

    The 2 first properties mean that all transactions are indistinguishable from
    one another. Unless you directly participated in the transaction, all inputs
    and outputs look like random pieces of data (in lingo, they're all random
    curve points).

    Moreover, there are no more transactions in a block. A Grin block looks just
    like one giant transaction and all original association between inputs and
    outputs is lost.

So I think "No more amounts" is simply trying to say that the concept of a globally-accessible transaction on the blockchain with a verifiable transaction amount is now gone. Now it's just blocks, which can be many transactions coalesced together. From later on that page "It's as if when Alice gives money to Bob, and then Bob gives it all to Carol, Bob was never involved and his transaction is actually never even seen on the blockchain." It is not trying to say that this currency is not countable or something like that (how would that even work?)

[0] https://github.com/mimblewimble/grin/blob/master/doc/grin4bi...