Unless FL has some unusual provisions, I believe the federal standard is that an opt out must be given prior to the actual checkpoint. In other words, there must be notice provided that a checkpoint is ahead, and some legal means of avoiding it must be available (a turnoff, for instance). Whether this is a mandatory USSC ruling or just one that is practiced in most other states I do not know for sure.
But, as long as one has not yet headed into the checkpoint, you always have the option to make a lawful turn. No stop can be made without reasonable suspicion, and assuming a turn is made lawfully, it should be irrelevant as to whether a checkpoint was ahead or not.
I Strongly suspect the turn was unlawful in some way, or something else gave rise to an unlawful act justifying the stop.
- Carl