Hell, I'd be pretty ecstatic to make the postseason this year lol, let alone make the World Series.
I think WS is a bit of a stretch, but I think the logic is also the fact that frankly, the AL in general is pretty bad this year and even some of the top teams like the Yankees are dealing with major injuries (Gerrit Cole TJS, etc.). Also, a lot of the projections are high on some of the Red Sox' young players performing well (Campbell, Anthony, Casas, Mayer later on, etc.)
Another thing is, if you did a power ranking of the entire league, the first 4 or 5 teams are all NL. Then it's likely Texas, Boston, Baltimore and New York Yankees in some order from the AL. The NL is loaded, but the AL not so much.
My prediction is, the WS will be Rangers vs. Dodgers, but I do believe the Red Sox will make the postseason and potentially even the ALCS.