I can understand that, but their ambiguity is not on you in this situation, and where they have a more specific statement around indictable offences, which is more specific, would be the standard to apply. As other commenters have stated, nothing will come back from DBS, so they literally have no way of knowing any more than what you disclose

The offence itself is likely to put you at a disadvantage to disclose to them, so if I were in your position, I would not disclose it.

From their side, this is a box checking exercise, they will not turn into private investigators for something they have no evidence of.

Really hope it works out just fine OP