You are correct, there was no mention of a camp. It was noted in his National Archives files and on his Find a Grave memorial that Maarten was arrested during a raid and died on 31 Jan 1945 in Zutphen, Gelderland, Nederland, aged 23. Based on experience this would have been for some sort of forced labour group.
PS: I have other relatives I have found in similar circumstances. I have looked at Netherlands, World War II, but no luck finding a suitable categorization; any help would be appreciated.