It isn't. The grammar is completely different from that of any other language (except, of course, Loglan).
I'd suggest that the grammar of Lojban does bear a significant resemblance in higher-level form to the grammar of predicate calculus, if not in the nitty-gritty surface of it, sufficient that it's worth mentioning alongside Loglan. It's certainly making things easier for me. But I suppose that is probably neither surprising nor relevant to many people. -Jonathan