Is that an anchor on the bow in the pic? Doesn't seem like a very big anchor; if it's right-sized then it would seem that the boat might not be all that big*. At any rate, NO TRAILER BRAKES is most certainly the secondary cause (first is driver fault [for, of course, not ensuring proper brakes; second would be for not allowing sufficient and safe braking speed/distance- even without trailer brakes one can stop a large load).
* Quick check of anchor weight (yes, this is a pretty broad description as there are different anchors with different holding capacities, but...), basing on a boat of about 40' in length and about 23k lbs (that's what I believe is about right here), would be something like 55 lbs.
I've run without my trailer brakes being hooked up towing maybe 3,500 lbs. I was careful. But I will NEVER do this again. Best practice is to always verify your brakes are working BEFORE you need to use them: anticipate an up-coming stop early- if your brakes have managed to stop working (after they were known to have worked) then you have some time rather than NO time to deal with the predicament.