I think they replied to the right one, making the point that the long comment about malware is missing the point about the type of keylogger this is trying to protect against (because many people also, quite reasonably, use the term "keylogger" as a vague description for password-stealing malware).

The top-level comment you replied to doesn’t mention malware.

In any case, both hardware and software keyloggers exist which would be thwarted by an onscreen keyboard. If I recall correctly, mouse keyboards became popular when keyloggers started being more known, and the following generation of malware took screenshots every time you clicked.

It’s a very obsolete security measure but did make sense briefly.