That looks like a DDoS, for instance that doesn't ever happen on my ISP as they have some kind of DDoS protection running akin to what we would see on a decent cloud provider. Not sure of what tech they're using, but there's for certainly some kind of rate limiting there.

3. Isolate the server from your main network as much as possible. If possible have then on a different public IP either using a VLAN or better yet with an entire physical network just for that - avoids VLAN hopping attacks and DDoS attacks to the server that will also take your internet down;

In my case I can simply have a bridged setup where my Internet router get's one public IP and the exposed services get another / different public IP. If there's ever a DDoS, the server might be hammered with request and go down but unless they exhaust my full bandwidth my home network won't be affected.

Another advantage of having a bridged setup with multiple IPs is that when there's a DDoS/bruteforce then your router won't have to process all the requests coming in, they'll get dispatched directly to your server without wasting your router's CPU.

As we can see this thing about exposing IPs depends on very specific implementation detail of your ISP or your setup so... it may or may not be dangerous.