Did they see the car decelerate? It may slow via regen w/o hitting the brakes. Sure, it feels like it is "slamming on the brakes" but it may not actually be doing that. For example, when the speed limit changes it will "regen down" to the new speed limit. It won't utilize the brakes.
For future reference, as soon as you touch the accelerator, any braking is disengaged and regen is reduced, so hitting it to 100% isn't really necessary.
FYI, on I-69, when the issue occurred (as previously stated, it may be resolved in new maps), there was a section where my vehicle would slow from 70 to below 45 for a while if I didn't override it (it may not have decelerated at full regen like some people experience, but it still did decelerate that much). I actually let it do this to show the service center the issue. There were no cars around when it slowed down, but I turned on my hazard flashers for the duration of the slowness, and several passed me before I finally overrode it. Interestingly, based on multiple trips, it wouldn't slow down again in the same area where it would have remained slow once overridden. It wouldn't slow down in the same spots with TACC, either, just with EAP. One could certainly argue that the driver needs to be attentive and not allow this to happen, making it less of an issue, but I think driving less than 45 on an Interstate where the speed limit is 70 is a dangerous behavior regardless.
supercharge.info doesn't show a permit or construction for Bloomington or Elberfeld, but both locations show end of 2018 as the target on Tesla.com. Depending on where the superchargers go in Bloomington, I would think you could be better off using the Elberfeld location. I have an HPWC at home, so that's the one I'm looking forward to.
