No, its not sunburn. Your Money Tree is doing fine.
Money trees are somewhat unruly plants that will periodically lose many leaves all at once even with the best of care. It grows fast always adding new leaves only at the tip ends of each stem. But indoors it can only support a limited number of leaves at one time, so when they max out they will shed older, lower leaves.
This leaf shedding does not usually mean the plan is unhealthy; it is just the way it grows. Poor light or improper watering can aggravate the problem, but that does not seem to be the case with yours. Overwatering is rarely a problem with this plant.
The only solution to this is to prune back leggy stems as they become tall and leafless at the bottom. Any stem can be pruned back to any height. New growth will emerge subsequently starting just below where you make the pruning cut and continue to grow upward from there.
Once any stem reaches your preferred height, you can simply regularly pinch off new leaves as they emerge on that stem thereby keeping it from getting any taller.