He did not obey the 100 meter rule!
§5 Overtaking (Author: VavelOnline)
This is a very simple how-to guide on how to overtake (and be overtaken) properly. The first thing you should be aware of is DESYNC. Basically, what you see on your screen is not always what the other players are seeing. This might cause (unintentional) ramming in many situations. To counter that effect, here's some practical information that you should always follow.
When overtaking
Start your overtaking maneuver when you are at least 60m from the truck in front of you (you can always check the distances using the TAB key).
Stay in line
When you checked that the other driver is 100m behind you, you can start merging back.
Alternatively, if you see the other driver turn its lights on, or hear him honk 2 short times, it means that you can merge back safely from his point of view, even if you're not 100m ahead. In that case, it's nice to thank him using the left-right-left-right blinker signal. Note that high beams would normally be used IRL, but cannot be seen for now in the MP game.