looks like slip knot to me also. does have benefit of not binding/ easy to loosen as well as quick and easy to tie. will jam on a teardrop thimble and i've never seen a round one.
According to the U.S. Coast Guard in their Boat Crew Seamanship Manual common knots loose much of the line's strength. The following table is from the above manual.
Knots or Splice Percent of Line
Breaking Strength Lost Percent of Line,Breaking Strength Remaining
Square 46 54
Bowline 37 63
Two Bowlines (Eye in Eye) 43 57
Becket Bend 41 59
Double Becket Bend 41 59
Round Turn 30-35 65-70
Timber Hitch 30-35 65-70
Clove Hitch 40 60
Eye Splice 5-10 90-95
Short Splice 15 85