Male passengers traveling alone usually fit the profile by Customs & Immigration in most airports as unusual & suspicious especially when he has very little to no luggage. Especially so when the airline ticket was purchased at the last minute.
Beautiful young female passengers traveling alone or together with other young female passengers & with no passport stamps from previous trips also fits the profile as unusual & suspicious of intending to engage in vice activities especially when the tickets were purchased at the last minute.
Airport officers also ask questions to assess the accent and language skill of passengers to make sure their nationalities and/or places of birth match their accent and language skill. If there are inconsistencies, the passengers will be considered unusual & suspicious of using a forged or stolen passports.
Unfortunately, there are plenty of law abiding travelers who fit the above profiles but were singled out for further questioning, screening, searches, and intimidation at airports. It's a very subtle type of profiling & discrimination being practiced by bureaucrats at airports worldwide.