I hear he was travelling alone and was kidnapped in the evening in Nioro, which is the malian border town. Kayes region, but far from city of Kayes.
I suggest he was spotted in Ayoun and they then prepared the attack.
A few years ago an Italian and his Burkina wife were kidnapped near Koubeni, south of Ayoun el Atrous. Also in the evening.
Bottom line - la Route d'Espoir isn't safe. Bad things more likely to happen as you come near the Malian border, and then no real security until you reach Bko.
One recruiting center for jihadists has been Boutilimit, which is actually on the road only some 170 kms east Nkt.
If you are going east from Nouakchott stay alert all the way to Bamako. Don't move around after dark. Check in with the military before nightfall. Don't hang around unnecessarily.

A better route would be going south from Nkt to Rosso and then east along the border river to Bogue-Kaedi-Selibaby. But there the tarmac ends and there is a sandy piste to Kayes. Alternative route is through Senegal. But going east from Kayes you will pass through Diema. Perhaps better go south and then east through the bush.

This kidnapping was according to a spokesman a conscious expansion west.
As there have been people kidnapped as far away as Tunisia before who ended up in Mali, it could happen in Senegal, Burkina or elsewhere too - don't you think? Only a matter of time, if nothing is done to stop it.
And now they say it will take a year to get started with the intervention.