I don’t think it’s entirely safe to assume that all democrats will vote for witnesses. In the case of a tie, IMHO, the vice-president would cast the tie-breaking vote.
The VP is not a Senator and in any case the conflict of interest is glaringly obvious.
51 to pass, 50/50 is a fail, and there are no Constitutionally qualified tie-breakers.
The author of the article needs to look closer.