Normally (as it's not always the case for all games -- but normally), when the game is playable from start to finish is the point at which the title will move from Alpha into Beta. Beta basically means that all of the critical mechanics are in place. Not necessarily everything I want to put in the game, nor that they're working reliably or well balanced yet, but that everything needed is technically there.According to this comment, the alpha milestone was completed a month before the original article (so in early April), and the game was playable from start to finish. But comparing that for example to the timeline of The Witcher 3's development, it would still point towards a 2021 release, which also seems to be the consensus among the employees in the article, only one person suggested late 2020 (and implying that it would be rushed then).
From what I've seen, there is still quite a journey ahead from this point. Lots of work getting everything securely in-place, adding in stretch goals, and polishing / testing everything as much as possible before it goes Gold.