I am certain you are right and I am wrong, but my brain just refuses to understand that LAN out is out to the LAN. I would have expected WAN out to go to the LAN (the 'vice versa' in the above: the traffic from the internet comes in on the WAN and goes out on the WAN to the LAN).
Maybe another way to think of it? Data arriving from the internet you are happy to call WAN In. Then what label/name will you give packets that are transmitted from the WAN to the internet (acknowledge packets, the Google search string you typed, the email you send, the text that you post here in the forum…). If the stuff coming from the internet is WAN In, then you are kind of forced to call the traffic in the opposite direction "WAN Out".
Once you have that convention, then packets arriving on LAN (=from LAN clients) become LAN In, and packets transmitted to LAN (clients) become LAN Out.
Then you just live with the convention, even if your brain struggles to cope sometimes :)