@nutildah, what Tryninja said is correct. The banner appears because the account has negative feedback that was created by a DT member before the trust flags were introduced. Theymos intentionally did this so warnings could be shown to guests even for users who received feedback from the past since no one was going to go back to thousands of past cases to create a flag for each scam accusation.
This is how the banner appears

After the introduction of the trust flag system, new negative feedback from DT members would not show the banner by default since members would have to create Trust flags
This is how a type 1 trust flag banner appears.

So the default banner for negative feedback by a DT member from the past looks like that of type 2 and type 3 flags to a guest user.
This is exactly what came to my mind too after reading nutildah's question, but that doesn't seem to be true.
If that message had been displayed due to the DT negative trust, it would have been shown for
this topic too.
Because that feedback from the DT member was after the implementation of the trust flag system.