Fabrication may take the form of inventing a new statement and attributing it to the Prophet ﷺ. It may also involve taking a remark from a pious predecessor or a wise saying and falsely presenting it as prophetic. Good meaning does not validate a forged attribution.
A third form is to take a report known through a weak isnad and attach an invented sound-looking chain so that it circulates more readily. The pre-existence of the wording does not make the artificial chain genuine.
Crucial distinction: discovering actual independent, credible routes may strengthen a weak report. Manufacturing an impressive chain for it is fabrication of transmission. The question is always whether the claimed attribution can be evidenced.