Odd highway sight

A couple years ago something very weird happened to me and my mom while driving. My mom picked me up from the airport in France. Since we live in The Netherlands it was a few hours of driving from the airport to our home.

This was around 1 at night. we were driving on a highway somewhere around Belgium. this region is basically covered with forest. I also remember it was raining heavily. When out of nowhere we see a gentleman walking on the side of the road. He had a suit on and a briefcase, no umbrella and soaked. he was walking in a straight line and did not move his head.

Because I was very tired it took me a second to realise and I asked my mom “did you see that too?”. she said “yes” and the whole way home we discussed the event and who this man was. It spooked us both and we still talk about it sometimes.

Did anyone ever see something like this or has a theory? I would love to know what you think.