Hello Isis,
My feelings are that the monk you'd met probably is a bogus one. To
my understanding, these bogus monks and those "8-precept ladies"
(those ladies in pure white clothing) seems to be controlled by
overseas syndicate.
Now firstly in Singapore begging for alms on the street is not a
common practice. Any local monks would know this. And if it is a
visiting monk, then he should be housed by a temple that he had
registered himself in.
Testing the monks by asking them to chant the sutta is rather
pointless, probably he may really know how to recite and whatnot.
But you can try for entertainment purpose. My friend did this to a
chinese "monk" who claimed he know many sutra. Then my friend asked
him to recite ended up he only kept repeating "Nan Wu(yes he
pronounced Wu) A Mi Tuo Fo" with that confidence look on the face.
My friend ended up calling police on the spot. And apparently in
his bags, there were cigarettes, condoms (the police was laughing
over this), passport, a small book that records how much donation
he had received and not forgetting cold hard cash.
Usually these bogus people often got away successful because they
prey on people's kindness; and some common people's perception that
"they-also-come-out-to-make-a-living-so-be-it". I think as
disciples of the Buddha we should be careful and aware of the
situation. Compassion should be accompanied with Wisdom.