So do I have this correctly? Jeff had a major infection on his machine? If so, how is Avast to blame for this?

its not this means he didnt have an UPDATED AV if any on his machine.
now that avast tells him the truth he doesnt like it.

this is why I wanted a AV for my macs even if there are very few viruses for them. there is still the chance (even if small) that my mac could contract one