Most manuals are written to cover their arses! even LED fairy lights for the Christmas tree probably have the do not use an extension lead disclaimer, it is fair enough as it is effectively a spur off of the ring main, and they don't know what else is plugged into it.
The 16Amp thing is probably foreign, most countries do not have a fuse in the plug end of the circuit, so discounting that a UK ring main circuit is normally 30Amp, though I know my friend in Sweden has a ring main rated at 16Amp , which has a single 20Amp cartridge fuse at the consumer unit (which is quite an odd looking construction)