IBM's response to Google called "On 'Quantum Supremacy'" has this to say:
"Because the original meaning of the term “quantum supremacy,” as proposed by John Preskill in 2012, was to describe the point where quantum computers can do things that classical computers can’t, this threshold has not been met."
In other words, "quantum supremacy" is not being used as just a buzzword.
So yeah, IBM is casting doubt on Google's claims of "quantum supremacy" because "supremacy" doesn't just mean "better than everything else."
"Because the original meaning of the term “quantum supremacy,” as proposed by John Preskill in 2012, was to describe the point where quantum computers can do things that classical computers can’t, this threshold has not been met."
In other words, "quantum supremacy" is not being used as just a buzzword.
So yeah, IBM is casting doubt on Google's claims of "quantum supremacy" because "supremacy" doesn't just mean "better than everything else."