It could well be - although it might depend on which specific partition you are talking about (boot or root).
You will probably want to boot Jumpdrive on the phone from a host computer. Doing that you can then examine the situation on each partition of the main disk of the phone and likely recover back to the situation prior to the update.
Possibly this procedure here: Can't use L5 after update! - #14 by mladen will get you going (but the version number in step 13 might be out of date).