@Tromos -- AVOs and their response to RF power.
Are you sure it was a genuine AVO meter?
The traditional AVO Meter uses a copper oxide rectifier as the AC rectifying diode NOT a point-contact germanium or junction silicon diode etc. Copper oxide rectifiers have a very bad frequency response which makes them cut off in the upper audio frequencies, perhaps 100kHz or so.
This fact is very useful (and well known to techies). If one had to measure [any other] voltage near VHF transmitter antennae etc. (i.e.: when one's up the mast near the antenna etc.), one used an AVO as it would NOT respond to the transmitted power. (I've used an AVO specifically for this purpose myself on many occasions.)
Most other multimeters use a point-contact diode which DO respond very well up to microwave frequencies and thus it would likely have indicated as you've stated.
Moreover, as the copper oxide rectifier as used in the AVO (Model 8s and earlier) was a hard-to-get replacement, when it was damaged some slack techies just replaced it with point-contact types (OA91 etc.) which worked but the calibration was somewhat buggered.
I'd suggest either the AVO wasn't a genuine AVO brand (and you're using the term generically) or it had its diode changed for the wrong type by improper service.
The AVO Meter was pretty unique in using a copper oxide rectifier (at least in multimeters made since WWII). I still own three of them which I still use when working in RF environments, they're invaluable (it's a shame they're still not made).