Actually... Broken company. This degradation in software quality is so widespread now.
My input here: I have the same problem. I had two such failing updates. Security-Update 2019-002 for Mojave, and Safari 13.0.4
I was lucky to find (thank Google - Apple's site is no help) the link to download the security update installer manually. So I did, and installed without a hitch --- this means, that the "network issue" is just plain wrong. Safari was perfectly able to download the same thing from Apple.
As for the Safari update -- I'm stumped, since I could not find any link to download it manually. the problem lingers on, and I just have nowhere to get the software from.
My suspicion is that this is yet another trick to "persuade" us users to "upgrade" to 10.15 (Catalina) and so lose about all our beloved, well-functioning old Mac software (which happens to be 32bit). I'm a Mac and iOS developer, and I have thousands of $ invested in great software tools - so I will never upgrade to 10.15. Not until all these tools become obsolete themselves.
Anyway, Apple software (even system software) is now failing hundreds of times a day. One can just open the console and browse the endless list of crashes, exceptions and other failures throughout the system to confirm this.