Yes

Btw, I wasn’t throwing the book at OP and I really hope my post is not seen or taken that way. He or she just kindly pointed out, as a warning to others, that you can get stuck if you enter the departure area and wish to leave without a good reason. This topic does come up from time to time and I was just pointing out that there is a legal basis for not being in a restricted area hence a reluctance on occasions for airlines to provide an escort.

“Bona fide passenger” is open to interpretation probably based on prevailing circumstances. That is possibly deliberate given that the exemption is not for someone “with a valid boarding pass”. I doubt that anyone would be prosecuted for using a lounge even if they intended to exit, unless things escalated if someone demanded an escort and got very difficult if the demand were denied. If that were to happen, someone claiming to be a “bona fide passenger” could find himself on the back foot.

The Singapore sign saying this is an “arrestable offense” is very direct but it probably reflects the same position as Hong Kong.