I don't know that I would jump to dyslexia at this point. Writing is still a skill that is developing and so I wouldn't get too worked up if he put the r before the o in orange. It's common to mix up and say 15 is 51 or vice versa. Kiddos are learning to discriminate.
Another poster in another question stated a great comparison. It's hard to learn to discriminate how one little change can make something totally different. She stated that a couch is always a couch. If you tip it over, move it to another room, put it upside down, it's still a couch. So it's hard to discriminate that 51 and 15 are 2 different numbers.
Also, if your child should ever need Special education services don't feed into the negative stigma. Sped is a GOOD thing intended to close the gap and help kiddos succeed. Good luck w/your little one :-)