no there are many forms, ranging from spelling wrong, to reading words and not understanding them to like you say reading backwards...there are different degrees of severity....my brother has the type indicated above....the spelling a word with the correct letters but the letters in a mixed up fashion
i have a mild form of this kind of dyslexia...where i spell some words with letters the wrong way round, or read them wrong...which is why i was so scared of reading out loud in class...especailly in biology when i might have had the word 'organism'