I think he was probably unlucky for it to be that bad, but I did see 4E frequently stretch on for ludicrous amounts of time once you got into the teens and especially with a larger party. We have six PCs, like fifteen monsters/NPCs, in a level 14 fight and it took two sessions to resolve, and I doubt there were more than 9-10 rounds in there. Sure it was a pivotal fight but it wasn't two sessions pivotal (they were short sessions, maybe 3 hours of actual play). If things ran a bit slower...Normally I would just let this go but since we all seem to be making a big deal about this.
If I assume a 5 person party, with an equivalent 5 monster party fighting them....which is a good solid "normal" 4e fight. That means that every single person here.....including the dumb as rocks brute monster that literally has 1 attack.....takes a full 6 minutes to perform their action.
How does it take 6 minutes for a creature to make an attack, roll some damage dice, and add them up?
I could respect one of your players having analysis paralysis (we've all been there), or having a really complex power and maybe taking 6 minutes, maybe even 10. But every....single.....creature on the board taking that long every....single.....time?
I could absolutely believe it takes an hour to finish a combat, I can absolutely believe two hours. But an hour for just a round....I'm sorry but that really seems like an exaggeration to me....or you are running a lot more PCs and monsters on average than I noted above.