Typical red LEDs used for displays have a peak emission somewhere in 600-650nm range, but it's bell curvish so yeah you can expect a small amount of 670nm light out of it.
Does getting exact 670nm light matter? It's just the wavelength that this particular study investigated. They do not offer conclusions for other wavelengths as they did not test them, it's as simple as that. But a lot of other researchers did, especially in red/infrared part of the spectrum and generally with positive results - http://bitly.com/PBM-database. So I would guess you should be able to get some of the described effect at nearby wavelengths as well. 670nm seems to be near an absorption peak of cytochrome c oxidase, a molecule believed to be involved in the mechanism of light therapy action, which is why I suppose it appears frequently in research.
Does getting exact 670nm light matter? It's just the wavelength that this particular study investigated. They do not offer conclusions for other wavelengths as they did not test them, it's as simple as that. But a lot of other researchers did, especially in red/infrared part of the spectrum and generally with positive results - http://bitly.com/PBM-database. So I would guess you should be able to get some of the described effect at nearby wavelengths as well. 670nm seems to be near an absorption peak of cytochrome c oxidase, a molecule believed to be involved in the mechanism of light therapy action, which is why I suppose it appears frequently in research.