This is not a vulnerability. This is simply btc1 nodes (which will fork off in a few weeks) pretending to not be btc1 nodes because they do not want Bitcoin Core 0.15.0+ nodes to disconnect from them. They fear that they will be disconnected from the network before their fork happens and don't want that to happen.

However not everyone is running Bitcoin Core 0.15.0+ so they will still be able to connect to the network via peers running older versions of Bitcoin Core. Furthermore, this behavior is bad for both networks; following the fork, they are far more likely to find themselves isolated from their network. They will be rejected blocks from their Bitcoin Core nodes because of the fork, but won't have any connections to other btc1 nodes so they can follow the segwit2x chain.

Only altcoins that will fork from Bitcoin in the future. Other altcoins are consensus incompatible with Bitcoin, so they could connect to Bitcoin nodes, but they will experience the same problem that btc1 nodes will face after their fork: they have no connections to nodes that are following their consensus rules.