I don't find that unreasonable at all in my opinion. Most wiki's even acknowledge this by having a boiler plate saying "this page contains spoilers read at your own risk". Dropping spoilers about any type of story is taboo even on fan forums regardless of how long its been since release. The expected place to talk about them is in private or under an area that is clearly marked plot spoilers (or at minimum a post with a spoiler tag that makes the text not readable).

Even if it wasn't the standard, at the very least its common human decency. If you enjoyed something wouldn't you want everyone else to enjoy it as well? Dropping spoilers of any kind in a public page without proper precautions is just being a dick.(note I do feel that the person in this case at least tried, it just didn't work well cause most would have to see it in order to read the comments under them, but an attempt was made so IMO they do not fall under this category)

Time since release has never made sense as a valid excuse for me. So we are just going to magically think that everyone knew it was released and had the ability to watch it sooner? Hell some don't even have access to the media to watch it sooner, either due to age or just lack of accessibility