Sinagpore Angle has a wrap:

…there is no law forbidding individuals using lawful means to
acquire historical material, the authorities decided to bring charges
of "spying" against Ching Cheong instead. In fact, Ching Cheong’s work
with the Straits Times and his receiving renumeration has been seen by
some officials as "receiving large fees from a foreign intelligency
agency"

Also see ESNW, where a grand unification theory is being studied:

Ching Cheong was not arrested in Beijing, which is the powerbase of the Hu Jintao faction.  Instead, he was arrested in Guangzhou.  Do you know who is on the Guangzhou provincial committee?  Ching Cheong may just be a sacrificial victim in a factional struggle in which the losing faction took revenge and placed the winning faction in public disgrace.

This theory is unverifiable and unfalsifiable from the information so far.

UPDATE: 4 June 05, 10:00: See also Daai Tou Laam for more links and comments, notably.:

The mainland regulations for journalists are so restrictive, that few foreign journalists bother to comply with all of the notifications of authorities. But the mainland officials will haul out the cumbersome regulations, that really are a throwback to the Maoist autarky, to detain journalists reporting on sensitive topics, like the riot in Zhejiang a month or so ago.