Well apparently that worked (for the teacher although not for me as admin).
However, he has now made another hotpot quiz and now this one isn't recording grades.
I'm finding it very confusing to try to find out what currently works and what doesn't. Would it be possible to have an up-to-date list of hotpot modules that do work within moodle (I don't know hotpot at all so it's difficult for me to tell which original hotpot he's used and therefore follow through with problems, if I could tell teachers which ones to avoid - for now - that would be a good start in debugging journey)?
Additionally, it would be great to know which ones should not be used because they are simply replicating moodle features. (I have a feeling the masher may be one, and I also have a feeling that might be the one I'm now having a problem with.)
Also, current state of play vis a vis versions:
I have used zip v1.3.5 from modules download
and replaced hotpot.php with file attached to forum discussion below.
Sorry to be troublesome.