Article author here.

Supermajority attestations and block finalization, as well as withdrawal queues, prevent long-range attacks. To attempt to reorg a finalized block (blocks are generally finalized after 6 minutes) you have to commit to losing 1/3 of total staked ether, currently several billion dollars.

The only participants who can equivocate (vote for two blocks at the same height) are active validators so there is significant economic value at risk to pursue such an attack.