Good clarification. Depending on the variant of English, "long e", "long u" and "long a" may or may not sound like diphthongs. They can be analysed as /ij/ and /uw/. Wikipedia puts them under "potential diphthongs".

https://en.wikipedia.org/wiki/Diphthong#English https://en.wikipedia.org/wiki/English_phonology#Vowels