Details are not at the top of my mind these years later, but you can probably rig something up yourself that looks like regular web dev shit and not a known commercial VPN. I think there was a preference in Firefox or something.
Countries like China have blocked SSH-based tunneling for years.
It can also block sessions based on packet sizes: a typical web browsing session involves a short HTTP request and a long HTTP response, during which the receiving end sends TCP ACKs; but if the traffic traffic mimics the above except these "ACKs" are a few dozen bytes larger than a real ACK, it knows you are tunneling over a different protocol. This is how it detects the vast majority of VPNs.
Source: used to work for a shady SEO company that searched Google 6,000,000 times a day on a huge farm of IPs from every provider we could find