Selig was not Danish but an American company and it seems that they both imported furniture from around the world and had its own production in the US: https://mrbigglesworthy.co.nz/designers/83/seligĀ
Having had a second look at the chair you linked to it looks like it was made using a dark stain, someting that was very rare i DK and looked upon as cheap and "poor craftsmanship". That, and that the design is so far from Kofod-Larsen makes me think it is probably not Danish. So for the origin you probably will find it to be from the US or similar, most likely with another name on it. Good luck with the research!
I hope yo will keep exploring good modernist design in this way. Or, perhaps if you feel adventourus, have a go at making your own designs?
"The good chair is a task one is never completely done with" Hans Wegner