No, the "-fold increase" form specifically means multiplying by that value, not adding that multiple of the value. A "3-fold increase" always means increasing to 3 times the original value, not adding 3 times the original value (which would be a 4-fold increase). See [1], the wiki link in the sibling comment to yours and many other results from googling "fold increase".
The percentage variant, in contrast, is indeed ambiguous, the "60% increase" mentioned in the comment I responded to ironically only being unambiguous because the purely multiplicative interpretation (going to 60% of the value) would be a decrease. Such ambiguous use of percentage changes is common and annoying, and it would be good to see more use of the unambiguous "x-fold increase" wording.
The percentage variant, in contrast, is indeed ambiguous, the "60% increase" mentioned in the comment I responded to ironically only being unambiguous because the purely multiplicative interpretation (going to 60% of the value) would be a decrease. Such ambiguous use of percentage changes is common and annoying, and it would be good to see more use of the unambiguous "x-fold increase" wording.
[1] https://www.collinsdictionary.com/dictionary/english/fold-in...