I COULD BE WRONG… BUT… My thoughts are:
It could possibly be that One Already established alliance or group left their original alliance temporarily and joined a half dead or tiny alliance and waited for war match making
The idea is, maybe they think that they are smart, by joining a tiny alliance or half dead alliance, The total alliance score will be alot smaller as Titan hits also count towards the total alliance score
This score during match making matches you with an equal ish opponent
Them being smart, or thinking they are smart think that by joining a tiny team, during war match making, they will be undermatched and thus helping them to win war super easily…
By the looks of it, that was an epic fail, your team started kicking buts and they gave up and left as any remaining flags wouldn’t make up for the rest of the points.
Maybe a strategy to join and start in tiny alliances, fight 5 straight wars wins, collect chest, then move on to the next one