If you're simply encroaching on their territory and they happen to have young they might respond to it as a territorial threat. I suspect it's direct threats to the actual young that trigger maternal aggression, in which case it's gloves off, you're going down. So while it's still the territorial type you need to back off, because you really don't want it to turn into the other kind.
I don't see much of a distinction between those two during mating season. A female with young has put significant investment into reproduction, and if the young has limited mobility, then female would benefit from lower threshold for threats and more active response in eliminating such threats.
A male that has managed to gain the top of the male hierarchy and claimed a territory has also invested significant in their reproduction, and since the territory and status is fixed, would also benefit from lower threshold for threats and more active response in eliminating such threats.
Its evolution based on passing on as many copies of your genes as possible, and the purpose of lowered threshold for threats and more active response is identical in both. Sex hormones are also a great tool to trigger this, but naturally in different context based on the reproductive method. It would also make a predictable theory that a species where both male and female have similar reproductive behavior and stakes, the relation between hormones and aggression will be similar for both genders.
The article claims that maternal aggression specifically occurs for pregnant mothers or while in the act of nursing the young (or at least while lactating). It seems that this is a very specific kind of aggression response, while the increased territoriality would likely be a case of defensive aggression.
