Theoretically, lightning can work without Bitcoin, but practically, it has little to no purpose. I presume that's what pooya meant. You'd use lightning mostly to avoid paying an outrageous amount of money for a low-value Bitcoin transaction, but beyond that it isn't useful. Litecoin's mempool is mostly empty, micro-transactions can take place there and get confirmed soon enough. Needless to mention that most lightning software is written to work on Bitcoin and isn't tested anywhere else.