Are they Messianic? There are Messianic Jews.
Orthodox Jews might not agree with Messianic Jews being Jews.
But they exist according to many Christians.
Remember that Christ himself and the apostles were all Jews. As a matter of fact, Christ was considered by many Christians the perfect Jew (in practice). He fought the corrupt Jewish leadership at the time.
"Messyonic jews" are almost always NOT Jews, but people like those described in this article who seek to deceive. They are non-Jews.
“Orthodox Jews might not agree with Messianic Jews being Jews.”
Depends.
If they are Jewish, then they are heretics.
If they are not, then they are (sometimes) frauds.
Most non-Jewish Messianic “Jews” are pretty honest about not really being Jewish. I don’t have a problem with them, provided they are honest about who and what they are. It’s not like I think following Jewish customs, practice, and law are bad for anyone.
In fact, I know of several notable converts to (proper) Judaism who came to Judaism from Messianic Judaism.
I view it as a great bridge between our peoples.