Mine are more closely associated than "same gallery", Jessica.
Right now I have a grouping of three, all from the same church. The first two keywords of each are bell tower,first congregational church; windows,first congregational church; windows, first congregational church. I do not have a "Churches" gallery. I do have a "Doors and Windows" gallery, but the bell tower one is not in there and, indeed, the word 'window' is not even in the keywords for that one. So what these three images have in common is the phrase "first congregational church" as the second keyword in their string and the word "churches" somewhere in their keywords.
They were visited by BH at 6:17, 6:18 and 6:18.
Interestingly, just before the first one, BH also visited another church at 6:17, this one in New Mexico. It's first two keywords are churches,new mexico.
So if that New Mexico church was visited at random, it seems that the bot was next "attracted" to other images associated with it.
I have been spending a LOT of time trying to get my keyword order to be meaningful. I'm only through just over 1/4 of my images, methodically checking them. I'd say about 1/4 of the ones I check are fine as is, about 3/4 of them require revision. This BH thing indicates to me that I may not be just spinning my wheels, and that's why I'm so interested. If the bots follow those thumbnails and the thumbnails are based on keywords and keyword order, a buyer might well be expected to do the same.