this article says that there has only been inconclusive evidence for infrasonic communication in giraffes. Perhaps they are just bigging up their own research, or perhaps it really is inconclusive. Who knows? (Well, David Brown probably knows....). There are further links within the article itself on the link below. What's making that eerie nighttime hum? (Surprise: It's a giraffe) - CBS News
Prior to this the only public evidence for giraffe infrasonic communication was a non-peer reviewed report from some zoo recordings, so this is the dawn of peer-reviewed scientific evidence for it.