Someone may know what it is but I don't. However, if all else fails, take a sample of it w/you to a lumber yard. If you can take a piece that's at least 1' by 1', they should have a pretty good idea what it is. AND, they may know if it contains asbestos.
I don't know of an INTERIOR type of 'paneling' that contains asbestos but you learn something new every day. If it was 1' x 2' in size or 1' x 3' in size, and it was about 1/4" thick and hard like cement, then I'd know what it is. If it contains asbestos, it's probably not that much BUT, nonetheless, can pose a hazard if not SAFELY removed and disposed of. Wait to hear what 'others' have to say on this Forum. Otherwise, try my 'all else fails' idea.
My best to ya and hope this helps.
PS: What's the dimension of the 'stuff', and how thick is it?