I could be very wrong here, but when I think of the 'isms (sexism, ageism, racism...), I think if you use more encompassing terms, all, most, none, few, then it tends to be more 'ist. "No women like MMM" - sexist.
If you're using (and thinking) in less absolute terms, I don't think it's that bad. "Many women like moneysavingmom.com" - not sexist. (IDK if this is even true).
MMM's quote could go either way, depending on his reasoning. "It surprised me because I am an engineer, and many women are not engineers" or "It surprised me because women don't like to get their nails dirty, and I do a lot of DIY."
But without that context, I don't see how his statement is sexist.