non hotbreak boilovers

So this is the first time i've experienced this:

had my wort boil over randomly about a half hour into the boil. had already been at a vigorous boil the whole time. It then tried to boilover again with about 15 minutes left.

I'm making an oatmeal stout and i mashed my specialty grains (biab style minimash) for 45 minutes @ 155F. Grains were

.5 lb flaked oats
8 oz chocolate malt
12 oz roast barley
1 lb caramel 60

I suspect the boilover was just from there being so many nonfermentables in this batch and a large amount of proteins.

Anyone else ever had these random boilovers? Is my theory approximately correct as to why it happened?

I don't think it was your ingredients, you probably just had a vigorous boil. Although the initial pre-hot break period is the time most likely for a boil over it doesn't preclude a boil over from occurring at a later date. I've had boil overs occur in the last five minutes if I wasn't watching the amount of heat I had going. Just adjust your temp next time and I think you'll be fine.

It can be benefitial to have something in the boil to help the bubbles form(like marbles, unglased pottery pieces or gravel)
Is there is only a smooth surface in the kettle then parts of the worth can get superheated and give explosive bursts of boil