I think the missing part from the person's post is not realizing there are variations of the watch. Some watches, like your, yea have cellular. I've got the 2nd gen Apple watch SE and I can't make calls off of it.

Although, interesting to know you had it on the series 4. I thought it was only on the newer series 8 and ultra, but I also just got my first apple watch about 4 months ago.