When I open drawings not done be me, line thicknesses vary from the thicknesses I have on my drawings eventhough both drawings use same template.
When I edit styles the layers show same thicknesses but the line displayed have different thickness.
Check your Drawing Tab under Tools > Application Options
There should be a Display Line Weight check box as shown in the attached picture.
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Otherwise it might be that they have altered (and overridden) the template settings for that particular drawing which can be checked using Manage > Styles Editor and selecting the Layers Tab. If any of them have been adjusted in the drawing, it should be quick and easy to see (this of course assumes that you have a library of defined styles).
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Finally, the individual lines could have been adjusted using individual overrides.
HTH