Now lowering the slats won't repair the sec's so the statement is quite logical. Lower the slats and you have max deflection again (35 degrees)
At < FL200 and < 150 KCAS the slats/flaps are available. Should the PRIMS/SECS be available, then it should be reasonable to expect the RT limit to be calculated as per normal. Otherwise, +/- 35° would seem to be the fall back compromise.
The RTLU setting was as a result of reversion to ALT2 Law, and whether other PRIM/SEC problems have intervened, or whether valid KCAS was available is simply guesswork.
EDIT :: Should the slats be extended as allowed below FL200, then any preset RTLU setting will not be cleared until < 150 KCAS, at which point the limit will be +/-35° and reducing if the KCAS increases again.