You are correct TB, because in the scene in The Don's office with Sonny, Tom, Mike, Tessio, & Clemenza, they are making a list and if you listen closely you can hear Clemenza saying : "it's a lot of bad blood. Sollozzo, Philip Tattaglia, Bruno Tattaglia; Garbone.." and then when Michael asks Sonny "You kill all those guys?" we hear Sonny reply "Hey, stay out of it, Mickey; do me a favor."

Now in that scene they are debating as to if the hit list is too much, too personal, etc. because we do hear Tom say : "It's too far -- I think it's too personal... The Don'll consider this all..." So it's quite possible that after some debating they eliminated some of the names on that list, with one being Bruno Tattaglia.

However, in the later scene, upon Michael's return to the Corleone Mall after getting punched by McClusky, Clemenza asks Tessio "What's with all the new faces?" and Tessio replies "We'll need'em now. After the hospital thing, Sonny got mad. We hit Bruno Tattaglia 4 o'clock this morning."

So it's quite possible that although they may have intially removed Bruno's name from that list, after Mike getting cracked by McClusky, and all the bodyguards outside the hospital getting locked up, Sonny lost his temper and they hit Bruno even though he was initially removed from that hit list.