It says as much on this page:
“The CNAME records should be set up with the DNS hosting provider of your domain name.”
NameSilo has a very specific area where you add cname records. There are two blank form fields. You choose CNAME or whatever, then you add the acme entry in one form field, then the other says “destination” and wants the destination string given to me at infinityfree. I’m surprised this is even an issue to be contested. It’s like a given that you have to set up cname records at namesilo that point back to infinityfree.