A fight can be stopped by body shots the same way a fight can be stopped with strikes. When someone gets rocked/falls down from strikes, typically the ref gives it some time, waits to see if the person can defend themselves, if they stand back up or maybe roll over to their back to defend from guard, anything.
To use an example, let's go back to UFC 153 where Anderson Silva dropped Bonnar with a knee to the midsection. Bonnar faceplanted in the fetal position and Silva went in for the kill, hitting him with 8-9 more punches before the ref stopped the fight. Bonnar was given a chance to recover, protect himself, or improve his position, he didn't and it was stopped. It was a good stoppage and I don't recall anyone complaining about it.
And that's what should've happened in the fight yesterday, the stoppage was way too early.