We got an old 2015 Macbook Pro (A1398) and I let Munin check if it is connected to the Wi-Fi network. When looking at the graphs I saw it was responding to ping packets even though it was sleeping!
A setting in the preferences application is responsible for this:
System Preferences > Energy Saver > Power Adapter > Wake for Wi-Fi network access
(German: Systemeinstellungen > Energie sparen > Netzteil > Ruhezustand bei WLAN-Netzwerkzugriff beenden )
When it is enabled and the Macbook is attached to the power cord, it will respond to pings in the network.
When the setting is disabled, it stops responding to pings 16-40s after closing the lid.