truck idoling while stop at store -I returned 4lo light flashing 4x4 not engaged

What is your question?

I stopped at the gas station and went inside and left my 2011 tundra crew max 4x4 idoling. I had taken my daughter to school and not been in 4x4 for several days. When I returned 10 minutes later the 4lo light was flashing. I looked at the knob and it was set on 2WD like I thought . I reversed fine and slowly began driving forward with light flashing I went 200-300 Feet and pulled off put in neutral engaged in and back out of 4hi without problem but light continued flashing. I drove about 1/2 mile with seemingly no problem and it suddenly stopped. I'm concerned about it due to the fact the truck was not moving or engaged in 4x4 hi or low and the 4lo surprisingly pops up.