Yup, Glenn has it right: in standard guitar notation, the "bare 7" is always a dominant 7th: a major triad with a minor seventh. Why? Because the dominant (V) chord is the chord most frequently qualified by 7ths--or 9ths, 11ths or 13ths. So if you consider the major dominant (V) chord rather than the major tonic (I) chord to be the default model for extended chords, you'll see why the 7ths are minor by default while the other intervals are major/perfect by default.

This model results in a concise notation for chords which is independent of surrounding context (key, mode, or role in progression), with the most common chords having the shortest, most directly understandable names. It is the convention I've seen followed in virtually every tutorial, song or tune book I've encountered--I can't recall a single exception. So I don't know why this should be considered "wrong". Those who think it's wrong are applying a faulty "consistency" rule that ignores the frequency of interval occurrence--and they defy a long-established, highly rational convention to little purpose.