If the tags were intentionally misleading, I would not consider that a spoiler.

However, I would probably avoid reading anything by that author in the future. Intentionally misleading readers using tags is something I would be very annoyed by.

Authors who feel strongly about not giving information out before a story is read should simply announce that they don't tag their stories or use story warnings, IMHO. Gaming the tagging system would push my buttons as a reader.