Nmap still shows “Host is up” after fixing the DNS issue — is this expected?

Hi everyone,
I’m trying to understand something about Nmap and network isolation.

I have an OpenWrt router with two separate networks:

**LAN**: 192.168.1.0/24
**Guest**: 192.168.3.0/24

The firewall is configured so that Guest clients can access the WAN, but should not be able to access the LAN. Guest clients can also query the router for DHCP and DNS.

I came across this YouTube video where the author discusses Nmap discovering the hostnames of devices on the LAN, apparently because of DNS resolution.

I tested this myself from the Guest network:

nmap -sn 192.168.1.0/24

and got:

Nmap scan report for iPhone.lan (192.168.1.135)
Host is up (0.0027s latency).

Then I disabled DNS resolution with:
nmap -n -sn 192.168.1.0/24

and got:

Nmap scan report for 192.168.1.135
Host is up (0.0022s latency).

So I understand that DNS explains why iPhone.lan appears instead of just 192.168.1.135.

However, I’m wondering about the **“Host is up”** part.
Is it expected that Nmap can still report Host is up even after DNS resolution is disabled? Does this mean that the Guest network is actually able to reach the LAN host, or is Host is up based on some other kind of probe that doesn’t necessarily imply normal IP connectivity?