Food definitely affects the blood glucose levels, actually what he eats is a mayor factor in his blood glucose that is why giving low carb food is so important, because his body will turn carbs into sugar in his blood. That being said, he has to eat, so yes after eating his numbers (and even those in healthy cats ) will usually be higher obviously if he had high carb food they will be higher than if he had low carb and will lower as time passes.
The reason that we make the pre shoot test withdrawing food for 2 hours prior to this particular test is so that the result won't be food influenced and we then can know if it is safe to give insulin but when doing a curve you want to keep his routine as normal as possible including food schedule so test every 2 or 3 hours (depending if you are doing a 12 or an 18 hour curve ) even if he ate so that you can see how he's reacting to the insulin dose he's getting on a normal regular day and again just no food 2 hours before his preshoot test
If you tested 1 hour after he had ate odds are he still had some influence of the food so his number was a bit high because of the food when you tested, given his numbers it is not too much of a concern but as his numbers go lower you do want to make sure he has not had anything to eat prior to his preshoot test for safety reasons
Yesterday that he didn't had dry food his numbers were a bit better but on both days his nadir (lower number ) was around +4 +5 which is pretty normal with Lantus, and then his numbers start to raise a bit but not much which is normal too so ok, odds are that you will need to raise his dose because his nadir is a bit high still, what protocol are you following?