Yes it is :
From John East:
“The actual circuit of the MM bass is boost only, but there is a twist. The way the circuit is configured has been done in such a way that there is bass cut when the bass is fully backed off.”
It's a Baxandall, boost only, design : the "cut" only effects the lowest, and highest frequencies by introducing high, and low pass filtering when the knobs are fully backed off.
There is no "flat" setting, because you're always incurring some degree of boost from the EQ, or some degree of roll-off from the high/low pass filters.
The 3 band has a true (ie relative) flat position.
The original hangtag manual that came with the bass in 1976 also said that the EQ controls were boost and cut and for a “neutral” sound to leave them at the center position.
None that I've ever seen.
The prototype was cut only.
Tom Walker redesigned it as boost only, and his nephew - Sterling Ball - created the 3 band, with the expressed intention of offering the ability to cut the EQ, and to allow control over the mid range.
The 2 band, and the 3 band are designed to correlate identically in one specific setting - that is :
2 Band
Volume = 100%
Treble = 100%
Bass = 100%
is the same as
3 Band
Volume = 100%
Treble = 100%
Mid = Centre Detent
Bass = 100%
You can see that if the 2 band had offered cut, the mid range would be excessively pronounced, or the EQ would have had to have different corner frequencies / a different degree of boost, and/or a different slope.
Sterling has frequently reiterated that the 2 band has always been boost only. You could always ask him again, or just look up some of his explanations on the EBMM forums.