You cannot take the paragraph you are quoting out of context of the preceeding paragraph -
In the majority of cases, a "Plus Flag" applicant will be guaranteed an offer at the minimum entry requirement. "Plus Flag" applicants need to be predicted to meet - or have already met -those grades, and have any required subject.
Unfortunately, we can’t make this absolute guarantee in every situation. For degrees where we assess more than academic grades, an offer cannot be guaranteed for all "Plus Flag" applicants and in those cases, extra credit will be given in the overall selection process.
The absolute guarantee they are talking about is the one in the previous paragraph of min requirements, not an offer. Ds clarified this with admissions staff at the open day. He and his gf both had a plus flag and applied to Edinburgh. He applied for MEng engineering she applied for law/politics joint honours. He got an offer, his gf didnt with 7As NAT5, 5As Higher and predicted to do well in 2AH, 2H in S6. She ended up accepting a conditional offer from Glasgow for an extra A in S6.