Is this the most outrageous statement in a book?

[D B Campbell]

I would assume ValVict. is talking of the assumption that the De Rebus was 1. actually read by valens; 2. dated so securely.

As I said, I would imagine that Lenski is being provocative, by assuming that Alan Cameron's 1979 theory* about your (1) and (2) can be taken as self-evidently true. Lenski really ought to have referenced Cameron.

* A. Cameron, "The date of the Anonymous De Rebus Bellicis", in: M.W.C. Hassall (ed.), De Rebus Bellicis. Part 1: Aspects of the De Rebus Bellicis (BAR: Oxford, 1979), pp. 1-10.