The formula for the new lengths is

LL1 = CTE*(T1-T0)*L1+L1 and

LL2 = CTE*(T2-T0)*L2+L2

where T0 is the reference temperature for the initial link configuration. I assume the CTE is the same for both links.

Perhaps the reason for the error in the simulation result is that Large Deflection was not turned on for this solution. That means the solution was computed with the small rotation assumption, but the huge change in link length causes a large rotation in the link angles which invalidates the small rotation assumption. Rerun the solution with Large Deflection turned on and I expect you will get the expected link lengths.