Welcome to the wonderful Birthdayshoes website.
I bet Phoenix is hot. There was an article in Runners world where the writer was training and had to take a trip to Phoenix. He got in touch with a running club out there and they started their morning runs around 3 am. LOL
To answer your first question yes walking heel to toe is very normal in these shoes. You are suppose land heel and then roll to the big toe. When walking both feet are on the ground therefore, the pressure and impact is very light and distributed. When you are in running that is very different because you actually have periods where nothing is on the ground. Check out Vivobarefoot on their barefoot tab. They have videos on barefoot running and walking.
Have you tried adjusting the heel straps on your sprints?
Your bf may have to get a bigger size, I would get him to try some if you can find the size.