The two are not connected. It may be that BF is subject to a fine from French authorities if it failed to properly advise OP. But, that has no impact on whether there are "extraordinary circumstances." There are few examples of NEB's doing anything about the failure to notify, so it is effectively not important for OP.

There are three entirely separate EC 261/2004 issues here:

1. Duty of Care - This applies from the time of the scheduled departure until the time of the actual departure offered by MU. Here, that is 2 nights in a hotel and the associated meals as well as transportation to & from the airport. If no vouchers were provided, OP should keep careful receipts and submit those. There will be a fight here, so keep things reasonable because it may be a very long time before one collects.

2. Service Recovery - OP is entitled at his choosing to rebooking under similar transport conditions as soon as possible, at a later date or to a refund. Thus, if offered the 18th and OP wants the 20th, presuming that there is space, he may have it. He is, of course, not entitled to the additional 2 days' duty of care. It may be that there is no space today, the 17th, and thus the 18th is the next service. There is also nothing suggesting that OP must be rebooked on another carrier because there are likely many available options to SFO.

3. Delay - Given that the cancellation has already caused a delay at SFO of more than four hours, unless there is an "extraordinary circumstance" OP is entitled to EUR 600. Thus, the essential issue is to find out why the flight was cancelled. In simplest terms, why was the flight cancelled?

Don't bother arguing with front line personnel. They are likely poorly-trained or trained to say "no" and won't help. But, do understand that if you take a refund and then purchase new tickets elsewhere and pay more, that you will not recover under the Regulation. This is not to suggest that you won't recover under other legal theories, but that becomes complex and perhaps very costly.

It won't help you, but in addition to your claim under EC 261/2004, you should also file complaints with the French and with US DOT over your treatment. This would not be a complaint for money, but rather to have the air carrier the subject of an enforcement action. While no one incident matters, perhaps your treatment is common and an accumulation of complaints will cause one or both sides of the Atlantic to act.