I don't find it hard to believe at all, ARM is a perfect match for many servers since it requires so little cooling and power meaning that more disks can be fitted in a server instead (as that article shows) or more separate servers can be fitted in the same sort of space.
I'm actually really excited by this and really hope that ARM motherboards come onto the general retail market as well as in premade servers. Given how good the power to performance ratio of most ARM CPUs are, just think of the power they can get out of them in applications where more power is available!