Red triangle of death 2x, then check engine light, then no warnings at all, p0303 cylinder 3 misfire

HI; about 170k miles, 2nd owner from 50k miles; had hybrid battery replaced by dealer 5-6 years ago, 12 volt replaced soon after.
Recently car seemed to lag a bit going up hills. Other than that fine.
Had driven 50-60 mph for 8 miles then a lot of stops, starts before red triangle occurred when turned car on. 2x in a row.
Then it disappeared and everything seemed normal next time turned car on.
Drove car 1.5 miles; check engine light on.
Drove car .5 miles no check engine light on.
Drove 5 miles no check engine light on.
All of this occurred w/in 1.5 hours.
Went to O'reilly's auto, they ran codes (this is after .5 miles where no check engine light appeared at all).
Codes: P3191 (engine doesn't start); stored. //P0303 cylinder 3 misfire detected, pending.
Just realized that sheet I was given with codes listed showed car mileage at 297k when it's 170k. Don't know what that is all about.
The last 5 mile drive was to dealer because that was the only safe place to leave car from Sat night to Monday a.m. I know they're diagnostic is about $170 and I shudder to think about what they might come up with.
Friend who knows re cars says that once red triangle appears it's basically alll over; says that means there's a problem w hybrid battery.
O'reilly's guy thinks it's a spark plug. He had this whole flow chart of 4 or so different things it could be with the 2 codes but I can't find where I wrote it.
There was a huge rainstorm I think just after the red triangle of death appeared and we haven't really had any big rainstorms since last spring. But that was after the red triangle appeared.
When I say "red triangle of death" I wish I had taken a pic of it but I was so surprised I didn't. One screen said like "emergency" or something and another said "trouble." I think.
Any experience with anything like this and whether it could possibly not mean anything or be caused by a sensor problem or something else innocuous?
Thanks so much