RF communication vs Bluetooth
Bluetooth is RF, because RF stands for Radio Frequency, and Bluetooth happens to operate at a frequency of 2.4GHz, which is within RF bandwidth. Bluetooth is just a protocol for sending data over at 2.4GHz.

In general, RF frequencies range from 20KHz up to 300GHz, and some are used widely and have their own name. So an "RF" transmitter can be anything really.

Regarding your question - Bluetooth devices are classified in 3 categories. To comply with your requirements, you would need class 1 Bluetooth transciever, since it can communicate at around 100 meters. 

Another thing worth mentioning is that it might be wise to pick a popular, widely used RF module, since you know it works and will be able to spend time implementing it nicely, rather breaking your head over how to get it to work at all.

Small and lightweight are not specifications. 100 grams, 200, 3kg? What are the actual parameters? What are the maximum dimensions? The best is to formulate requirements SMART, Specific and Measurable being the key here.

Security does not necessarily have anything to do with the way you send data, rather how you encode it. My guess is that using a non-standard frequency would add another layer of security, but that is definitely not the most important thing.