I didn't realize that there was a belief on anyone's part that Aldi wasn't a national chain. Did y'all think it was only on the west coast?
Um, I've lived on the west coast and have traveled fairly extensively and have seen, to my recollection, exactly one Aldi store. I think it was when my wife and I went to SoCal for a concert over Memorial Day weekend this year.
In looking at the store locations, they are concentrated in SoCal with nothing (at first glance) north of Fresno or so.
Which makes sense, as we actively avoid all things LA basin-ish as much as possible (traffic, smog, crush of people, it being LA and all, etc.), so it appears that they have been popping up down there since we stopped going to that area somewhat routinely about a decade ago (we used to go visit with my wife's family in Huntington Beach every year around Thanksgiving and take our son to Disneyland, back when he was young and it was much more affordable). Looks like the first one in CA opened in 2016.
In fact, there are also no stores in Oregon or Washington. So "west coast" is a bit of an overstatement, unless you think LA is the only thing between Mexico and Canada along Highway 1.