That's what they claim, but the real reason is economic. Biotech means doing a better job with fewer farmers. The European attitude is that crops exist to employ farmers, clothing exists to employ weavers, wine exists to employ vintners, etc. Anything that threatens jobs is to be shunned.
Of course, now they're realizing that biotech threatens their sinecures whether they adopt it or not.
That may be part of it, and a bigger part of it for the EU is that they need some excuse to put trade restrictions on US agricultural imports. This is very convenient. They can pretend that it has nothing to do with trade, just public health and safety.