it is second "layer" as in a layer that only works on top of another (main) layer which is the on chain bitcoin transactions.
wrong
1. LN uses HTLC's for payment not bitcoin CLTV's
2. the denomination(unit of account) of LN is Msat which is something bitcoin does not accept
3. LN can function with just swapping(hot potato) msats using lite wallets that do not api/RPC a blockchain
4. if you were to API/RPC a blockchain your node can use the chainhash of litecoin, vertcoin or others. not just btc
it is not for "many blockchains" instead it is designed and is working on top of bitcoin.
5. refer to point 4 above
6. LN is a single network where multiple nodes can communicate where ach node can designate a different chainhash, to allow swapping on the same network
but like many other things that bitcoin starts, other altcoins copy and run their own as they are doing now. that doesn't change the fact that LN is a network built for and on top of bitcoin.
LN was built and then bitcoin had to change and get a new tx format to be LN compatible. also litecoin added this tx format before bitcoin did, thus technically bitcoin copied litecoin
have a nice day