Congestion doesn't mean just 'having' trains. It is relative.
5 trains within one hour may not be congestion for a passing station as all trains will just pass through the station, and there won't be any crossings involved.
But...
more... 5 trains in an hour may be congestion for a junction station where the trains will have to switch directions or cross over the main line into the branch line.
Yes, freights don't need platforms. But if it is a single line and a freight is coming in the opposite direction, or if there is a freight crossing over the main line, blocking the passenger train from entering the branch line at a junction, then the passenger train will have to wait at the platforms only. And if there are delays, this becomes even more problematic.