How do we distinguish between BTC and BCH in an address?
How do we distinguish between BTC and BCH in an address?

By looking at the post-fork BTC and BCH blockchain transaction-journals independently.

What does this &quot;the address also contains&quot; really mean?

They are saying that in both the BTC and BCH blockchain transaction-journals there were unspent transaction outputs associated with an address that existed in both.

Do they only mean that the transactions are committed before BCH, BTG, and BSV forks happened?

That seems most likely.
Incidentally, since many addresses are created deterministically, I suspect it is possible that re-use of the same keys in both BTC and BCH wallets would cause either to generate the same sequence of addresses post-fork. I am not familiar with BCH and don't know if they continued to use the same HD algorithm, it seems possible.