The convention is to give a fork a new, different name. The neomutt fork did so by calling their project "neomutt". So far so good.
I'm surprised and disappointed to see that Debian as of now has chosen to conflate the two projects and pollute the namespace. Renaming Debian's "mutt" to "neomutt" will ensure that each project receives the proper attribution and attention, and ease triage. Name squatting is silly and pointless. Kind regards, Job