The key word to your question is "Reasonable Cause". With the tape they are likely to have the cause to hold two of you for police.
The mechanical restrain is very reasonable. There is no torture. You are very lucky that your friend tried her luck in mall. If this is in a old casino between 50s to early 80s, you might be able to swim with fishes in the Lake Mead with a stone tight to your waist.
Camera is a very tricky thing. As long as her action can be viewed from public, camera coverage can be use as evidence. There are experts who makes good living on cameras, I am sure she is canned.
Police want to save paper work by having her pay for the items. Plus, if your friend can not afford the item, there will be a motivate of the crime.
You and your friend are embarrassment all Chinese around the world.