My five penn'orth:I'd think the van was following another vehicle which suddenly swerved to the left, causing the van driver to lose focus for a second..shyte parked car nowhere to go.
Happen a lot, especially when following big vehicles..
As for the Lambo..ahh well
2 second gap on main roads, 3 second gap on motorways... only change lanes to pass on the right and pull back in again when the other lanes are clear, unless all 3 lanes [or 4 in the case of some] are equally full as happens on average speed check areas.
if someone pulls out into the gap in front of you then you have to ease back slowly without braking to maintain the gap... no excuses. You should have space to slow down and stop in the distance you can see ahead, and know what's to either side and behind you at all times if something unexpected happens. It shouldn't be necessary to need to brake on motorways in normal free-moving traffic.
If the situation arises where someone gets angry with you, undertakes and pulls back out in front then you probably don't need to be out in that lane anyway, unless all lanes are full of traffic at similar speeds. If someone wants to break the speed limit and go faster than you are while you're passing a line of slower traffic then pull in when you can and let them past.