N900/Maemo 5 also uses Linux 2.6.28. "-maemo2" is the kernel EXTRAVERSION name and does not necessarily refer to the Maemo version. Based on the kernel version and build date, I'd guess that it's based on Fremantle or an early version of Harmattan (Maemo 6, pre-MeeGo). It could be a Columbus/RM-581, Dali/RM-680 (N950) or RM-660. Good luck booting the OS without an initrd!