The X11 license (MIT has used multiple licenses so there is no single "MIT license") does say "The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software." but not doing so is not theft.
The grandparent poster is correct -- copyright infringement is not theft and the two ought not be conflated. https://www.gnu.org/philosophy/words-to-avoid.html#Theft explains why: "Under the US legal system, copyright infringement is not theft. Laws about theft are not applicable to copyright infringement (http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&vo...). The supporters of repressive copyright are making an appeal to authority—and misrepresenting what authority says.".
The copyright holder in this case has options including suing, but calling what happened as "theft" is not an option and is unlikely to get anywhere with a judge.
“Courts have distinguished between copyright infringement and theft. For instance, the United States Supreme Court held in Dowling v. United States (1985) that bootleg phonorecords did not constitute stolen property. ” - https://en.wikipedia.org/wiki/Copyright_infringement#"Theft"
The original BSD license did have a credit clause which led to considerable trouble and controversy, so they don't do that any more. IANAL, and this is extremely bad manners on someone's part, but no laws were broken.
That's the copyright notice. The license text is "this permission notice". So no, you can not leave the original author name off.
The BSD license differs in that it requires the resulting software to display the credits, not just the source code to contain it. (Which is why e.g. phones or cars have somewhere deep in the menus a point where they show license information, to fulfill the BSD requirement)