The owner of a Google Sheets can tick off the option: "Viewers and commenters can see the option to download, print, and copy". However in this option, Google does not explicitly say that viewers cannot copy.

How are they able to copylock a spreadsheet and is there a way to bypass and copy anyway?

Here is a test spreadsheet:
https://docs.google.com/spreadsheets/d/1DLeK4X4MFbQe6X6lcbE_O-rTdy3MHApZEu1HhUWIji4/edit#gid=0