I'm unsure if this is intentional or a bug. I've done my best Google work, but cannot find anything on the issue which leads me to believe it is a bug. I'm running a Dell XPS 13 Developer Edition (9360) on an up to date version of Solus (as of November 15, 2016). Suspending using the on screen button, closing the lid, and pressing the hardware power button (which is assigned to "suspend") produce the same result. When the machine wakes from suspend, the system is immediately usable without the need for a password.
If this is intentional behavior, I believe this is a security risk. Especially for laptops, which are mobile and can be easily taken. I've looked into the settings and the dconf editor and found no option to require a password after suspend. If I recall correctly, other distributions allow this feature to be toggled and the default behavior is to require a password. Regardless of defaults, the option would be nice.