I can't see other users' private messages.
In theory you are correct, but these days a signature that breaks the limits in terms of height rather than width is a more serious issue, this is basically because more people are using wider resolutions these days so wider signatures are more lenient on.
His signature is fine to be honest, there are even some upper staff signature who are wider than they should be.
If it's taller than the limits, then report it. If it's wider but now on a massive scale, then you can probably leave it.