After much debate, we are agreed that the knot is a close relative of the Hunter's Bend. It may in fact be a Hunter's Bend, as there are a couple of different descriptions of how to tie it, one of which results in the above knot. It is one of a family of knots comprising two interlocked overhand knots. It is probably quite strong, and secure.
I didn't (and wouldn't) abseil off it. There's no need. I came across this knot again on a sling in Devils Pinch Canyon last year. I retied the sling with a double fishermans.
There are a few reasons I wouldn't abseil off it, but the main one is that I don't recognise the knot. And because I don't recognise it, I don't know how strong or secure the knot is.
Another reason is that it is difficult to identify. It looks like a Hunter's Bend. But then I tied a Hunter's Bend and another similar knot, comparing it to the pictures, and it was neither of them - even though it was extremely similar. I managed to replicate the knot after maybe an hour of trying, and it was nothing I could find in any reference. Easy identification and confirmation that you have tied a knot correctly is a good reason to use knots such as figure-8s, EDKs and Double Fishermans. It is also a reason not to use the Alpine Butterfly Bend - it's not easy to tell at a glance that it has been tied correctly/
If you want another reason not to use knots that can be easily confused, look up the Thief Knot!