Why is there a red light in green laser?

Your green laser is actually an 808nm IR (Right at the visual limit of red) laser pumped down to 1064nm IR and then doubled back up to 532nm green. What you are seeing is leakage of the 808nm laser diode output that in better constructed units would have been blocked by an IR bandstop or green bandpass filter. When the output of the laser is reflected or diffracted, the various wavelengths are split up allowing the near red to be separated from the dominant green. What you are not seeing is the 1064nm leakage, but rest assured it is still there.

When looking at the green laser output, your iris can detect and adjust for the intensity automatically, prompting you to turn your head or close your eyes if it is too bright. Reflected IR is not seen by your iris control loop so you can look at it until you are blind… frog in the cook pot style.