However, given the current system, it seems odd to me that they give credit (if we can call it that) for pretrial detention based on detaining the person attempting to flee.

The sentence is based on the crimes they were convicted of, including any aggravating factors. In this case it was a plea deal, so some charges were dropped in exchange for a guilty plea to the remainder.

Time spent in prison on remand is counted towards any eventual custodial sentence because anything else would be outrageously unfair. Not least because the court system grinds so slow, many are held on remand for longer than any eventual sentence (assuming they’re convicted at all).