“Infallible” does not mean “sinless.”
What is the name of the church you have found that has no sinners in it?
“Infallible” means “incapable of error.”
A “sin” is a violation of moral or religious law, which would be an error in that the commission of a sin required either ignorance or apathy in adhering to the law, both of which are errors.
So yes,being infallible would tend to lead one to believing that the church is without sin. And since the church defines (for themselves) what canon law is, hey, it isn’t as tho they can claim ignorance of their own law.