You get this achievement by finishing custom blueprints from other players on any route in the game. Head over to a race starting point (circles on the map) and go for exhibition race. There will be a preset race and from time to time another blueprint to the right that says "randomgamertag presents" instead of "horizon presents". Finish the race for the achievement.
Custom blueprints do not always show up, but you can force them to appear most of the time. Select to set up your own blueprint and tap RB to get to choose one of the car groups. Take one (for example hot hatch) and complete the blueprint, no further adjustments needed.
Instead of racing your own blueprint and getting
for that, there should be another custom blueprint from some random player to the right.
Edit Oct. 6th. people barely see blueprints from strangers at the moment, but it helps to have some friends who play the game and set up blueprints. feel free to add me or someone else (for example top players from the TA club in game, as they are active and will have some blueprints)