At first I thought that any reaction involving diazo group intermediate was a Sandmeyer reaction (i.e diazo coupling, diazonium substitution etc.) but I've been told a few times that a Sandmeyer reaction is only the reaction in which an aryl diazonium group is replaced by a substituent. Is that true? What about when an alkyl amine is treated with nitrous acid forming an unstable diazonium group which is replaced by a substituent?