I think it depends and I think the study more accurately reflects how rumination can escalate anger, not that venting doesn't reduce anger.
If one normally keeps it bottled up, then the occasional venting helps to reduce the pressure of keeping it bottled up and in my experience can break the cycle of not being able to let the thing go. If someone vents in a way that allows then to ruminate less over time then it is a benefit. As this study and previous studies were described, the person who just vented their anger was found to still be angry immediately after they were intentionally ruminating on the thing that made them angry. That is like measuring heart rate immediately after exercising.
I do think the study showes that ruminating on things that make us angry does work us up more than not thinking about them. From personal experience venting about something I have bottled up does reduce rumination starting an hour or so afterwards.