What can I infer from similar accuracy using two different DNN architectures?
I believe the only way to make a science-backed inference, would be if you fine-tuned both of your proposed solutions, to ensure that both are performing at their maximum potential. Only then you can say that method A is better than method B, otherwise it might just be a matter of improper selection of parameters that leads to those results.

However, if both methods still yield similar results after you have fine-tuned them, then you can follow Occam's razor and select the simplest one as the best one. By simplest, you can consider the one with the least amount of parameters and least time needed for training/inference.