The discussion was taking place in a Risk Management seminar and came up almost in passing. The comment was met with more then a few wide eyed stares as I'm sure you had when you first read it.
The Lead Investigator may have been reaching when she was stating these things. It sounded to me, and my colleagues, as if she was stating a long standing truth with FDA and that this was not 'new' ground and didn't go into much more detail.
I agree that the end user may not know what a 'Class III' device is but the Investigator certainly did make that leap.
She did not specifically say that you would be forced to submit a PMA for the device. She did state that if your company 'knows' that your device is being used in a class III device you are now responsible from a regulatory stand point for either bringing your device to class III status or having contraindications in place.
I cannot say that this is common knowledge as it was completely new to us. We work under the same understanding as you have outlined above. It certainly outlined a gap in understanding between this Investigator and the understanding in the industry as I could tell by the reaction in the room that everyone BUT the Investigator had your understanding.
I brought this to this particular thread because it would support what the original poster had heard and it may be worth it to bring it to FDA or your notified body for clarification. I know that I forwarded the information to my management as a 'this is what I heard from FDA today'.