I think that what you're seeing may be fairly common on snakes, but you're only seeing it because your snake is white & it shows up. The reddened scales are all
in a row, which appear to be from them getting bent backwards & bleeding a bit inside, probably from your snake scraping or squeezing into a tight spot that just
'caught' his scales a bit. So evaluate your cage "furniture", or stay up all night watching what he doesor better yet, don't worry too much about it. It's right
up there with a child stubbing their toe, IMO. Above all, teach your snake never to back up, so his scales won't "catch" & bend...(yup, I'm joking!)