Here is my layman, unofficial viewpoint on this. When I was mining LTC a few years ago, LTC to BTC was positioned as similiar to how silver is positioned to gold. BTC was much higher in value, the difficulty value is much higher to mine as well, hence a more sophisticated equipment is needed to mine for BTC. LTC was therefore being developed and touted as an alternative that’s easier to mine and cheaper in value. Therefore, that’s where the positioning of being complementary to BTC came about.
Hope this helps. Perhaps other veterans can add on to this. Cheers.