Oscilloscope analysis of the Honda 1000 and 2000 has been on the web for years now. Assuming (rashly) that the genset is in good working order, they put out OUTSTANDING quality AC and can't be blamed for damaging anything, any more than "evil spirits" could.
OTOH, even Honda states that their 12VDC output from the same gensets is intended to be used for battery charging only, it is a really ugly (impure) DC output that can and will damage electronics. They're honest about it.
So perhaps your expert has gotten the AC and DC facets of the Hondas confused. Or perhaps he wants to sell you something else.
But the objective and repeated results, from O'scope tests, say that Honda's AC output is simply not capable of doing that kind of damage. Unless, of course, there was a gross failure. Your local Honda shop--or ham radio
club, or tv repair ship, etc.-- can easily confirm that by hooking up to your Honda and seeing just what it is putting out.
You CAN easily get an objective and certain answer to this. Apparently your repairman is simply incapable or unwilling to use the right equipment
to do so.