It is marked NSFW on Lemmy and on the official yiffit.net instance site which runs Lemmy software.
You are on Kbin. Kbin is finicky at the moment with NSFW tags. Some posts get the NSFW tags with it, some do not. It is also newer than Lemmy and in early beta. It needs more bugs worked out. I am sorry it is not listing as NSFW for you, but it is tagged appropriately on my end.