Seems like someone told him to keep it up to seem more legit, yeah. If we had this picture of him as some skater kid from California playing Elvis, it might be weird, so PR was probably like, eh, keep the Elvis schtick up for a while, but just dial it down to a 6. 

It's still wild to me that the guy from Carrie Diaries was not only in a Quentin Tarantino movie, but is now playing Elvis in the biopic about him. But, what's even wilder is that Austin seems to be pulling an Elizabeth Holmes, lowering his voice for... legitimacy? Masculinity? I'm not sure why exactly, but his voice is completely different in all his recent interviews: 

Austin Butler's pulling an Elizabeth Holmes

Allison Piwowarski

When You Text "Nice," What Are You Really Saying?