By inspection of that photoset I see what look like four bolts that attach the backrest beam to the uprights. Those are going to carry effectively all the load when you are pressing, transferring it to the uprights via shear.
I have to guess, let’s call them half inch bolts.
Area of a circle is pi R squared. Each bolt has about 0.8 square inches of steel for a total of 3.2 square inches. Whatever you press plus something like half your body weight will be acting in shear on those 3.2 in^2. Let’s call that…500 lbs on a good day?
Force = load/area so 500lbs / 3.2 in^2 = 156.25 psi. I don’t have a book with me but a quick google search puts a single half inch bolt around 900lbs shear capacity.
You’re “golden.” Pun way intended.