In the preorder video, at the end they state that people new to battletech and who like strategy games will love this game.

At the same time that implies that people who are familiar with battletech, like myself, won't love it.
So.... wonder why?

Was it dumbed down from the way the originals worked?
... the board game worked?
Or was this just a coincidence?

I think they are just saying that if you are new to Battletech, which is several decades old IP with a rich history/lore, that this game would be a good spring board into being introduced to the Battletech world. That basically they are not going to make you feel like you need to do so much research into getting immersed into the world.

I believe this game takes place during the same time period as the first Battletech table top game takes place in. So it stands to reason that this would also be a good place for newcomers to start as well.

I don't think it implies what you think it does at all.

One of the things is that the mechanics are NOT the same as the boardgame, as some people hoped. So if you're familiar with the original Battletech board game, you're likely to be disappointed that the game is not exactly the same.

They tweaked things like autocannon damage (it's way higher than in the boardgame, where in the 3025 timeframe most AC's were rather crappy for the tonnage invested), there's a stability value which is decreased by repeated hits, making long-range-missiles somewhat capable of staggering and basically stunlocking enemy mechs, there's special abilities for the pilots, the line-of-sight rules differ, and a myriad of other changes.
Which might make your average Battletech-grognard who has been playing with the original rules for 20 or so years by now throw a hissy fit, since "they changed it and now it sucks!!!!"

I'm cautiously optimistic that this might be a good turn-based game based on the Battletech franchise. But I'm no diehard fan of the boardgames, and as such not really invested in the IP or the boardgame mechanics.

It appears to be similar to the tabletop game in spirit and in many mechanics but they did make some changes, it is not a direct clone.