I can't really comment on this development without spoiling the next comic, so...
A GUIDE TO UNDERSTANDING TEDD! (Confetti)
"99% Sure" in Tedd speak is basically "I have zero sincere doubt about this, but we haven't tested this extensively, and I have to acknowledge that I could be mistaken".
"90-98% Sure" in Tedd speak is where there's some doubt, but not so much to keep Tedd from feeling like they've probably got it right.
Anything below ninety Tedd will refuse to acknowledge as being confident about, and 100% technically doesn't exist, but is essentially acknowledged with statements like "in theory", "assuming the value of these variables are as expected", etc, so on, and so forth.