As in "yeah, those people only _claim_ to be christian, they're not _actual_ christians". It's a textbook example of No True Scotsman.
The idea that there is only one kind of christian died the moment that Mr Iscariot did his friend a bad one. Ever since then, there's been schism after schism after schism. Even Peter and Paul saw and did things differently. In the modern day, we're talking about rivalries so deep that even moving a ladder[1] is proven impossible, so how "they're only _claiming_ to be christians, and aren't _actually_ christians" passes muster, I don't know. These are the heads of christian sects going back more than a millenium, who disagree on what it means to be christian. Folks who are in charge of multiple large houses of worship, with large congregations that see them as their christian guides... but somehow "oh, I don't think they see it right, therefore 'not christian'"?
"No True Scotsman" is perfectly appropriate.
Rather, No True Scotsman requires that someone change their definition to exclude counterexamples while maintaining that they're keeping an untainted definition.
It's entirely legitimate to say "There are people who call themselves Christians but do not act in accordance with X, Y, and Z teachings of Christ. Therefore, I don't accept their claim." That's definition, not redefinition.