It is - but is basically a cropped version of the 4:3 which is how open matte works

I'd read the blu-ray release has this movie in widescreen

Warner have a nasty habit of putting their open matte ratio films in full frame 4:3.
The Vacation films, Moonwalker and The Shining all suffered the same DVD fate
With others like Beetlejuice they gave the option of both.
With 'open matte' though you are not missing any width, just gaining height. The picture is shot 'full frame' (4:3) but has excess headroom so the picture can be cropped to 16:9 widescreen.
Spielberg uses it a lot, and it was useful for films not being pan and scanned when put onto TV and video in the pre-widescreen days.
Only problem is you occasionally get a boom mic when shown in 4:3.

If you're talking about the DVDs I thought the same thing, seems a bit weird to have all the other movies in widescreen but not 4 and 5.