Absolutely not true. I was pre-selected by Delta and have used the Pre-check lane a number of times without a Trusted Traveler Number in my profile. I only have my name, gender, and birthdate listed in my profile. They sent out an invitation email to those who made the cut. Initially I believe it was Plats and higher, but later Golds reported getting the invite as well.
The above is correct. I am not enrolled in Nexus, Privum, or Global Entry. When the TSA Pre-Check program was announced a few months ago I was invited to "opt in," which, as I recall, consisted of checking a box or replying to the Delta email and making sure I had the necessary info in my profile. The letter said that participants in the trial program could qualify either by being PM or DM or by being enrolled in a program such as Global Entry.
Since I heard nothing further (there may have been a vague message about the start of the program at MSP) I wasn't certain I was really in the program, but when I flew out of MSP a few days ago I was selected for Pre-Check that day. Since selection on any given day is apparently random, now we can obsess before each trip about both upgrades and Pre-Check!