Uncle Vic is right to say that plate was originally a term which referred to items made from sterling silver. This was before electroplate or Old Sheffield Plate had been invented. For instance, you can easily find old books on Church Plate. These books are about Church silverware - not electroplate.
Old Sheffield Plate and Electroplate were / are techniques for making items that look like they are solid silver (plate) but are not. That is where the plate part of their names comes from.
Over time, people started to refer to solid silver as silver or silverware and old sheffield plate and electroplate as plate. As such the meaning of the word plate changed.
So, today silverplate and silverplated and plate are usually used to refer to electroplate. However, as mentioned before, you may sometimes see old books that use the term plate to refer to silver but in this case, they will not use the word silver.
Whoever told you this…
is an idiot and should be ignored!!