I've never heard anyone refer to themselves as Hebrew and it would likely weird or even offensive to most.
Hebrew is a modern language (and also an ancient biblical term for the people of that era).
Maybe your friend means he considers himself culturally or ethnically Jewish (a
Jew) but does not practice or affiliate with some, most, or any of the religious tradition (
Judaism). That would apply to some degree to many other folks, too.
Maybe the confusion or conflation of these terms is a part of it, as well?
Peace & blessings
7L
__________________
Bound by conventions, people tend to reach for what is easy.
Here we must be unafraid of what is difficult.
For all living beings in nature must unfold in their particular way
and become themselves despite all opposition.
-- Rainer Maria Rilke