Did you grow tomatoes there or close by last year or the year before?
I’ve got some tomato volunteers this year but I grew tomatoes there last year too so I know where they came from.
Compost that didn’t get real hot that had seeds in it will also do that.
And as mentioned, any critter that digests seed and then disperses them out the other end will do it. That’s why you have to be wary about manure sources.
I got horsenettle several years ago from some horse manure. Got rid of it but I have it again. This time it’s from hay from a different source but he has horses.
Not in that particular part of the bed. Very weird! But I'll take it. I'm just glad Beelzebub's Buddies (a/k/a gophers) haven't made their verminous way onto my property -- yet. Heh.
I've heard that horsenettle is horrible to try to eradicate because it keeps coming back. Reminds me of Johnson grass, which is almost impossible to get rid of once it gets established.