I'm not 100% sure but all signs point to this being the case. I have used multiple Bluetooth unlock proximity apps in the past and they all do the same thing. They throw up their own lockscreens in place of the real one. I am fairly certain that, as mentioned in this same comment "family", that this lockscreen is less secure than the system lockscreen. There was speculation that this might not engage all the security mechanisms like disk encryption. If I were one of the developers of this app I would be first in line to tell my visitors/customers that my product didn't compromise at all on security. Unfortunately, I don't recall any such claim on their site (if I'm wrong please let me know, I'm on my phone).