Worked at JPM previously. Don't think that's the case.

Even if we assumed the other candidate was offered on the day you had your last interview, it'd take at least a month for that chap to be onboarded (giving time for background checks and the other guy serving his notice period) - and that's the best case assuming his notice period is just one month.

It's more likely the recruitment wasn't treated as an urgent hire. Anyway, did you accept the offer eventually? What dept was the role in?