As to the gear anomaly - is it not true that the weight distribution in most pax jets is about 92% main gear, 8% nose gear? Seems like that would make it easy for the nose gear to "hop" while the main gear "crunched."
As to the cause - as scifi alludes to, runway friction (with ice) was apparently about 60% of that reported to the crew, and possibly even to ATC itself. (.27 vs. .44)