It sounds like you have assist turned on and it was activated during that time. I've never had my phone think I was driving more than 30 seconds after I get out of the car. Anytime assist is on (to announce messages etc.) There will an icon on the top left of the screen. Flick the notification shade down and there should be "I'm not driving/in a meeting etc. to click and it will disable it. Hope this solves your issue.
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