bitcoin Network Clients seen in the last 24 hours
only 99 connections ?
It is not 99 connections, it is as you said it in your first line the "clients that they saw in the last 24 hours". When you run a node, it will automatically connect to other nodes at random to sync with the rest of the network. This site is a block explorer which also runs a node and that node has connected to the list of IP addresses you see there.
It is not running a crawler to check all the nodes like bitnodes.io does, it is a simple node connecting to random nodes. That is why it doesn't have the accurate number of available nodes.
