Not nessisarily true. This is moreso stating Hasting's current and future rank, and the seniority within said rank. For purposes of commissioned time, and for when to grant the annual pay increase, 20 Aug will be used as the date he was "commissioned", even if he does not actually recieve his commission until months later.
Actually, looking at some of his other posts, it specifies that he is on leave without pay until Sept 7, so that date would be the one used.
Pay grade can be, and likely is different. Typically, DEO officers start off being paid on the 2LT scale immediately. In some cases, they may even be at an elevated incentive category, as occured when I enrolled. At the time, those joining DEO with an engineering degree started off being paid on the 2LT scale at the 2nd incentive level. (I'm unsure if this is only for those oging into trades that require them.) This policy may have changed, but again, looking over his posts, it does not appear that Hastings has an engineering degree, or is going into an engineering trade, so the point may be somewhat moot.