It is not particularly wise to draw far-reaching conclusions from the size of free RAM, in particular on Linux based systems.
Some used RAM can be anytime freed if necessary (cached/buffered/shared), otherwise it will enhance the general responsiveness of the system.
The Linux kernel manages RAM great, so you shouldn't worry about free RAM, unlike on Windows systems. If the system needs more RAM, Android will find the best possible way to produce it through removing really unneeded processes and services from RAM.
It can happen, that it seems you've got no free RAM, still the system is pretty responsive.