They’re not overly preoccupied with Judaism or Jewishness (is that a word?) per se… rather, a flavor of Christianity that places more emphasis on the Old Testament (among other things) than most…
…particularly its portrayals of a punitive, authoritarian God, as opposed to the tolerant, forgiving God of the New Testament.
NOTE: Technically, the punitive authoritarian God and the tolerant forgiving God can arguably be found in both Testaments if you look for them.
EDIT: Also, everything PioneerShmioneer said.