This is not snake venom...

This is a protein that binds to the same receptors as a particular snake venom because of homology (the reactive site has protein similarity). It was almost certainly by design. What it is not is a "venom" it's a "virus." Not that the distinction here is all that important, but "anti-venom" has nothing to do with it specifically. Anti-venom is a specific monoclonal antibody that binds to a specific protein region. Monoclonal antibodies are very specific. In the case of SARS, you can have many different monoclonal antibodies that will work (binds to different parts of the SARS-CoV-2 virion). If the particular one for the snake venom also works on SARS that's great (though I'd be surprised if it works very well since the similar region is not large).

There are also many other treatments that can be used on a virus though, not just monoclonal antibodies. Things like HCQ, Ivermectin, etc. are likely even better than monoclonal antibodies (not to downplay its effectiveness).