They might have noticed it (too late) that they were on the taxiway but was it safer to continue (due to snow, smaller strip etc).
To the KLM/Dutch bashers: Who is telling you it was a (all) Dutch cockpit? Not only Dutch are flying for KLM...
(big chance it was, but that we'll find out when the report is published). Who ever they might be, it should'nt have happend.