You are missing the point. Based on the fact she was not seen after she left the house, the BF's word is all they have on where she was going, yet she never made it there, and IF he did not pass a LDT, that is all the probable cause they need for a SW. I don't know whether he passed or failed, I'm saying IF.... that's all.
I am in no way saying that the BF is a suspect, BUT they have to take into consideration that he is the last known person to have seen her.
My son has been in LE for over 20 years, and I know how easy it is to get a judge to sign a SW, it can be done in ten minutes.