blocking icmp outbound to the internet, or to your gateway (ie pfsense) from your own network seems beyond cut off blood to your brain tight tinfoil hat..
Even when I lock down my guest network and prevent them talking to anything on any my other networks, I still allow them to ping the pfsense address of the network they are on - this allows them to validate connectivity to their gateway.. And how that wifi is working as far as basic connectivity to the gateway, etc..
But to the point at hand - lets see the logs your looking at.. Whatever they are in, so we can hope to clean some insight to what its actually saying vs what you think or stating its saying. Maybe your firewall on your machine is blocking your machine from trying to ping that IP? And your reading it as inbound block?
Hard to guess without actually seeing what your seeing. If you believe its coming in from something else on your network than a simple sniff on your device showing this traffic will allow us to see the mac its coming from which we can then trace to what device its coming from on your L2 network.