Not only because SegWit, but because more people
adopt & use SegWit. If all bitcoiner use SegWit, we will see far lower transaction fees and always 1-block confirmation.
More info :
https://www.reddit.com/r/Bitcoin/comments/7rrb3w/day_9_i_will_post_this_guide_regularly_until/I think Bitcoin fees have reduced recently. Is it due to Segwit?
I think so?? Maybe? but i read some articles that they are on test net they implement Lightning Network already and i hope that the transaction will reduce fees.
No correlation since most people use LN in testnet for testing/development purpose, only small amount of people who use LN in mainnet (which is risky) and you still need make on-chain transaction when open/close channel and refill balance.