Is it? It doesn't say so anywhere in the datasheet.
Jfet opamps are usually characterised by an input bias current in the picoamp range. The LME49990 has an input bias current in the range 30-1000nA which is more typical of a bjt input.
See page 190 of Horowitz & Hill.
You're probably right. I don't remember where I had heard that, and having just spent about 10 minutes looking, all I could find was a reference indicating that the 49880 (not the 49990) is a jfet dual.