Searched the web for quite some time and still can't find a solution.
Is it even possible at all to restrict ssh user to a single directory in 10.11? I have set up an user account via System Preferences Users & Groups. Under Advanced Options I specified a home directory. This is the highest level directory he can go.
Followed some instruction to modify ssh/sshd_config to include:
Match User ftpuser ChrootDirectory <the directory path> PermitTunnel no AllowAgentForwarding no AllowTcpForwarding no X11Forwarding no
but it doesn't work.